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We both know that you're not going to read this section (that has no technical information) the first time you see it but I ask you to come back and read it soon. It really is important information that will help you navigate through the thousands of files included in this tutorial.

A Working Through the Content

The Quick Links menu at the top of the directory is for use after you've become familiar with the information on the various pages. To most effectively work through the tutorial, start with the Safety page, just below the - Directory - Repair header. Work down from that point. This will make the information easier to understand than skipping around.

B Resizing Content

I don't think this is news to anyone but I'll post it anyway. For those who are unaware, you can change the size of the text and images easily by holding the ctrl key down and rolling the mouse scroll wheel (or using + or - buttons on the keyboard). The shortcut ctrl-0 resets all. Try it now if this is new to you. If you'd like, you can make the content of the left pane completely fill that pane in this way. In some instances, you'll want to search a long page. If you go to full-screen (F11) and resize, smaller, you can scroll a lot more quickly. When you find what you're looking for, find the number it corresponds to in the list. Click one of the 'Back to the Top' links and reset the size. Then click the number in the list to go back to where you need to be. If there are no list numbers, highlight and copy a short segment of text. Resize and then perform a ctrl-f search for that text. The reason that the two options are needed is because the zoom can travel quite a ways from the point where you are when zoomed out. Other Navigation: For these to work as expected, you may need to click in the frame you want them to work in (main or directory) to have them work as expected. Home Key: The Back to the Top links are generally best, where available, but the home key will get you to the top of the page (maybe higher on the page than you wanted to go, if you're looking for the menu). The BttT links are especially helpful for those who are working away from a computer desk (i.e. on the shop workbench) and may not have a keyboard immediately available. End Key: Same basic function as the home key but it brings you to the bottom of the page (where there is often a Back to the Top link). Page Up/Page Down Key: These step approximately one full page height per click and will repeat if held down. Insert Key: This one can cause confusion because there is no indication which mode it's in. Try not to click it. If you accidentally do and you try to edit text, what you type will overwrite whatever was to the right of it. To complicate matters even more, it's not recognized by all software so where it interferes with one program, it won't with others. PrtScn Key: This one copies what's on the monitor. Alt-PrtScn captures only the active window. These copy to the Windows Clipboard. Then you paste them into something like Irfanview, edit as desired then save as the file type of your choice, in the location of your choice. Type .PNG is often best for captures with sharp text, .JPG is better for captures that are more photographic in nature. Scrolling Long Pages: Some of the pages are long and using the scroll bar handle at the right of the frame may not work very smoothly. If you click your center/mouse wheel button, the cursor on the screen will change and moving your mouse up or down slightly will scroll smoothly. The distance you move your mouse from the point where you clicked will determine the scroll speed. After scrolling, clicking the mouse wheel again will clear this mode of scrolling. Background Color and Font Options: For those who are really interested in this type of work, you will spend significant time with the tutorial. To help make it better for you (visually), there are now options for font and background colors. Previously versions of the tutorial had strict font control but in recent re-writes, the control over the fonts was largely left to your discretion and will be whatever you choose. Arial or Verdana are web-standard fonts. Those two are OK for short periods but not for extended reading. If you have it, Gulim is a very fine/thin font that sometimes works better than the two previous suggestions. The likely default is 'Times' which is hard for me to read for long periods. Depending on the monitor, fonts from 14 to 24 pixels may be options for various readers. My preference is Gulim at 20px and that's what's set in the .css file (it can be changed). If you find yourself using the zoom feature (ctrl-mouse scroll wheel) often, you can change the default font in your browser. THIS page (more important than you might think) has several examples if you're not familiar with fonts. If you're using one of the browsers (other than the recommended Safari or Chromium portable) that doesn't allow you to set a suitable font or adjust the font size (Maxthon browsers or the older Opera 12.14), you can set the font face and size in the .css file. Email me at the following address if you need help doing this. babin_perry@yahoo.com New options for the background have also been added. These options are not quite as simple as clicking a button but they only require that you: 1. Open a .css file in Windows Notepad (nothing else). 2. Copy and paste a number or name into a specified location (simple). 3. Save the .css file and reload the tutorial page to see the results. Change until you find what you like the best. Remember that links for both the background and font instruction pages are at the top of this yellow table and that this page is the second one down from the top, in the directory.

C Flash Content in this Tutorial This should have been resolved before you purchased the tutorial but if it wasn't...

This tutorial uses Flash graphics extensively. If you're using a mobile device like the iPhone or iPad, it's likely that you won't be able to view most of the interactive content because many of those devices can't display Flash graphics. Using the right hardware and software: To get the most from this tutorial, use it with a standard desktop or laptop computer with a full-sized monitor and a mouse/trackball. Use a Flash-capable browser. If you contacted me before purchasing the tutorial, it's likely that we've already confirmed that you have a suitable browser. If you want to find a different Flash-capable browser, go to THIS page or email me at: babin_perry@yahoo.com There may be instances (in some browsers) where you may not be able to enter values into the Flash graphic text fields if you try to enter them where the graphic resides on the page. If that happens, click the link below the graphic to open it in its own tab. This should resolve the problem. If not, email me. Possible Monitor Options: Today's monitors are typically in a wide-screen format and generally best suited for watching movies. They are not really formatted for viewing long pages. To see more, at one time on your monitor, you can go to full-screen mode. To toggle full-screen mode, use the F11 button/key. This will increase the effective height of your monitor. If you're familiar with the operation of computers and hardware and are using the tutorial on a high-resolution, wide-screen monitor (which the tutorial doesn't need), you may want to rotate the monitor 90° and use the monitor in portrait mode. This is done by some who code or produce large vertical text documents. Do this only if the computer is exclusively used for the tutorial. It may not be suitable for daily use for other content. I finally got around to doing THIS after repairing a monitor that needed capacitors (huge surprise :). It works well but takes a bit of getting used to. If the monitor in portrait mode isn't quite wide enough to fit the two frames, there are a couple of simple options. One is to grab the frame between the main and directory and drag it over toward the directory. The other option is to right-click the link in the directory that you want to open and select open link in new tab. There is an Easter egg in the directory cells. If you click the upper corner of the cell, that will open that cell's link in a new tab. Above, it was stated that you don't need a wide-screen monitor for the tutorial. An older 19" 4:3 monitor with a 1280 x 1024 resolution will work well (for normal mode, not portrait). Larger than 19" is a bit better but not necessary. I used an old Dell computer with a monitor on an articulated wall mount. The keyboard and mouse were wireless but I so rarely used the keyboard, it was only important that the mouse be wireless. If you have a neat workbench, neither needs to be wireless. What made it work so well was the articulated wall mount for the monitor (monitor had a VESA mount). Many people use laptop computers but with that, you lose all of the bench-space taken up by the keyboard of the laptop. With the wall mounted monitor, you lose absolutely no bench area and the monitor can be pulled in close when you need to see fine details on a diagram or datasheet. The vertical display may not be everyone's choice but the rest of the suggestions work well. Side note... If the only option is a laptop computer, you can do this with an external monitor plugged into the laptop. One last note... The most basic, 10 year old Dell or HP computer running Win7 will do all you need, to use the tutorial. Ask around and you'll likely find people willing to give you computers that are just taking up space. Pre-Loading: This pre-loading will work anywhere in the tutorial (except the Quick Links) and will prevent waiting for pages to load. If you want to open any/all of the tutorial links in background tabs so they will load and be ready when you switch to them, right-click >> open link in new tab. Flash: The embedded Flash files have advantages that make them useful. The vector aspect of the graphics means that they are essentially infinitely scalable. They will remain sharp, regardless of the magnification. They will, in some cases, contain large raster (photo) files. These take significant resources when used at high resolution. Many of the pages with these large files will cause slower computers to hesitate when you scroll over the large files. If this becomes a problem, grab the scroll handle and scroll the full length of the page several times quickly, the browser will store the files in RAM and from then on (until you leave the page), the page should scroll smoothly. For all Flash files, you can zoom in (right-click and select from menu). To navigate when zoomed in, use the left mouse button (click, hold and drag). When opening a Flash file in a new tab, go to full-screen mode (F11) or at least maximize the window. The various Flash diagrams can be printed at high quality if you open them in the stand-alone Flash player (if you installed all four Flash Player files). For many Flash diagrams, there is a link to open them in the new tab. If you copy the file name from the address field, find it in the tutorial files, in the Windows file manager and open it by double-clicking it there, it should open in the stand-alone Flash Player. From there, you can print it. Remember that you're not limited to printing to paper. You can print to PDF and other formats. The options are likely in the printer options dialog box. When you open a Flash file (extension .swf) in the stand-alone Flash player, it allows printing but there is another option for a small number of .swf files. There will be a .exe file with the same base file name as the .swf file. Many people will panic (for good reason) when they see a Flash-related .exe file. These files are harmless. They allow printing if you don't have the stand-alone flash player installed. Your anti-virus will likely warn you and scan it when you click on one but all will come back clean.

D Mains Voltage and Damage to the Scope Ground

The Term 'MAINS': You will see the term 'mains' in the body of this tutorial. The term refers to the AC voltage supplied by the electric utility company. In the US, it's 120v, 60Hz at common wall outlets. Another common mains voltage is 230v, 50Hz. There are many others. Connecting a mains-powered scope's chassis ground clip (generally connected via a banana connector on the front panel of the scope) or scope probe's ground clip to anything other than a 0v ground can damage the scope because the scope's chassis ground is typically connected directly to the mains ground. The GND on the scope in THIS image is obvious, as is the probe's ground clip lead. For many 12v power supplies with 3-prong power plugs, the front panel output 'ground' terminal is also connected to that mains ground. If you connect either of those scope grounds to power source (±voltage) inside an amplifier, the scope and/or the amplifier could be badly damaged because that voltage will try to pass through to the mains ground via the 3-prong mains power plugs. You'll essentially be shorting that supply voltage to ground. This can lead to excessive/damaging current passing through the scope's ground circuit because the large bank of capacitors, charged to high voltage stores considerable energy and that energy will be discharged into your scope. THIS page has information that will help prevent you from using a damaging ground point for your scope.

E My Shorthand

†: You will find an unending number of dagger (AKA obelisk, or obelus) symbols of various colors. These allow explanations of various pieces of information without having a comma-enclosed comment several sentences long inside a paragraph. There may be 10 yellow daggers per page but the small dagger (with paragraph text) and large dagger (below, on its own) open/close that colored pair. If you see another small dagger of the same color later on the same page, look for it's larger mate shortly below it (could be several paragraphs or images below). ~: If you see the character '~', it means approximately. For example, ~15v means approximately 15v. ±: If you see the character '±', it means positive and negative. For example, ±15v means positive AND negative 15v. This is commonly used when stating the output voltage of the various power supply circuits (±15v, ±rail voltage, etc.). B+: B+ is the positive battery terminal connection on the amp or the positive 12v source (depending on the context). TNFG: TNFG means Take Nothing For Granted. Confirm everything that could make a difference for the circuit you're troubleshooting. Make no assumptions. xxx: If you see a part number that has a lower case 'x' as part of the part number but the other letters of the part number are upper case, it means that there are several versions of the same basic part. For example the TLx94 could be a TL494 or a TL594 but, for the context, they are similar enough so that the TLx94 would cover both parts. The same goes for the L7815, L7805, L7809.... If the context was for the L78.. regulators in general, they would be referred to as the L78xx regulators. Weeds: You'll see 'a trip into the weeds' (or something similar) throughout the tutorial. These are (generally) short tangents with something that may be of interest. It's not generally completely useless information but may not be perfectly in line with the more relevant content on the page. For long paths through weedy areas, you'll generally have an option to skip over it. Part Number Clarification: If you see a lower case 's' at the end of a part number (particularly one that has other letters in upper case), that's the pluralization of the part number and is not part of the part number. For example, If you're instructed to replace the 'IRF3205s' in the circuit, the part number is IRF3205, not IRF3205S. There may be instances where you will see something like IRS21844S. The capitalized S suffix is part of the part number. IRS21844Ss would be plural. There will be instances where multiple pins of an IC will be referenced. Let's say it's a TL494. If the pin referenced is pin 14 (which is the 5v regulator output pin, by the way), it may be referred to as 494-14. If there are multiple TL494s and they are designated as IC601 and IC602, that same pin of IC602 may be referenced as IC602-14. PDF Page Number: You will have to use PDF files with the tutorial. If you see it written that you need to go to 'PDF' page xyz, that means the number in the page indicator on the toolbar of the PDF reader. There are instances where the numbers on the original printed document don't match those of the PDF file. This should make it clear on what point of the document you should be looking, for the information. Map Reference (MR): In some documents like PDF diagrams (and maps), there are numbers across the top/bottom of the page and letters down both sides of the page. These are used to give a reference location on the page. This helps you to give the location of a part that may be difficult to find. For THIS diagram, if you were told to check Q126, you may be able to find it quickly (maybe) but if you were given the page number and the location/reference of page 1, F6, you could go directly to it. If you're using PDF Xchange Viewer, zoom out, align the horizontal and vertical markers (they show mouse x-y positions) to F and 6, then use ctrl-roll mouse scroll wheel to zoom in on that point. PDF File Links: There will be instances where you will click a PDF file link and it will open in a browser window. The application used by that browser may not be ideal. The file location will be shown in the browser's address field at the top of the browser window. You can: Navigate to that folder and double-click the file to open it in the default PDF viewer Or, copy the entire address, open your PDF viewer, choose the 'open file' option and paste the entire address into the file field at the bottom of the window. Or, copy the entire address, open the Windows file manager (Windows Explorer, File Explorer) and paste the entire address into the address field at the top of the window and click enter. This will work for any files that have a default application associated with the file type. Recommendation: PDF Xchange Viewer. It's fast, free and works very well. You should have installed Safari for times like this. Safari is FAR superior to other browsers when you will encounter files/folders and PDF files. Other browsers open the PDF files in a generic PDF browser. Safari opens it in a Safari window but it opens it in your default PDF application. This retains all of the features you expect (including being to navigate with the hand tool). Safari !! If you see a horizontal rule at the top of a page that is colored like the one below, instead of the normal gray, the page will be nearly impossible to use, as intended, with anything other than Safari. [ ] PDF Viewer Access: If you want a quicker way to access your PDF viewer, there are several options. The easiest is to pin it to either the Windows Start Menu or the Windows Taskbar. In Win7, all you have to do is right-click on the PDF viewer in the list of software/applications (instead of left-clicking, to open it) and select pin to either the Taskbar or the Start Menu. You can also send a shortcut to the desktop. Same process as before but you select Send To >> Desktop (Create Shortcut).

F Use the Suggestions as Starting Points

There are many tips in the tutorial. Most work well for me and probably will for most people. Use them as a starting point. You may (will) find a way to perform some tasks in a way that will work better for you... but, when first getting started, don't spend time TRYing to reinvent the wheel. Instead, spend time learning the material. Although many tips will be in sections for a specific type of amplifier, don't let that give you tunnel-vision. Many of the tips can work for other amps, as well.

G Markers

For sections that contain checklists, important information or graphics, I've added markers. For text... copy the text between the markers and paste it into a text editor (Word, Notepad, Wordpad...). For items that cannot be copied and pasted, there will be specific instructions. Print the items and keep them handy for the first few repairs. If you see a '•' next to a link in the index of a page, that indicates it's a section where you'll find the markers.

H What You Need to Know About the Links

There are many links to other pages. Many times, the link is to a point in the middle of another page. If your computer's hard drive isn't fast enough, the place where you land may not be precisely where you want to be. This means that you won't see the information that you're expecting to see. If the page loads in the same pane of the browser (to the left of the directory), let the page load completely (will take 3-4 seconds) then go BACK and click the link again. Generally, the second time you go to the page, you'll land in the correct location. For pages that open in a new tab, let the page load, close the page then click the link again. For those who cannot get the page to load properly, I generally have the name of the page and the item number on the page. It will look something like this: flameproof and fusible resistors (Resistors and Capacitors page, Item #6) For links (both images and entire pages) that pop-up new tabs, close the new tab (ctrl-w is often quicker/easier than using the mouse to click the x) after your done with it. If you click another link and the pop-up window is in the background, the linked page will open in the background window and you may not realize it (leading you to think it's a dead link). 'Ghosted' Text: There will be some text that will be barely visible (like the 'Back to the Top' buttons/links that you'll find on many pages). The text is generally non-critical and could be insignificant comments, options/links... If you left-click and drag to highlight the text, it will become clearly visible. 'Ghosted' <I: If you see <I where you would expect to see a blank space, it's a snippet of information that will show up in a balloon if you place your mouse cursor over it. Highlighted Links in the Directory: There are some links in the directory that have a rectangle around them. These links are for pages with a heavy load (multiple Flash files and/or a large amount of content). These will take longer to load in Safari. The left-hand pane may turn white or seem to freeze until the page loads. For Safari, the wait can be up to 10 seconds for loading (but will depend on your computer), the first time you visit the page. After that, Safari should cache the page so subsequent visits will load more quickly. Types of Links: The following applies to the pages where all links are color-coded. There will be some links that open in new tabs. You can close the new tab after reading the pertinent information. There will be no 'back' option on these tabs/pages. When you click a link that doesn't open a new tab, it's likely that you're being redirected to a point on the same page that you are on. In those instances, selecting the 'back' option will get you to where you previously were. A link with this color underline is an external link and best used with Chromium portable. Expect Safari to fail for any external (pink) links. These are typically the only links outside the tutorial files. A link with this color underline is a link to a pop-up image. In Safari, it will open a new tab. To clear it, close the tab. In Chromium, it will open a pop-up window which needs to be closed. A link with this color underline is an internal link. It will open a new tab. To clear it, close the tab. A link with this style (gray) underline is an internal link but the content is on the same page that you're currently viewing. Clicking that link will bring you to the relevant point on your page. This is the only type of link, for most of the pages of the tutorial, where the 'back' button will be used to bring you back to the previous point you were viewing. External Links: The two most common browsers for the tutorial are Safari 5.1.7 and the portable version of Chromium. I like Safari but some of the external links won't work with it. Using Chromium portable may eliminate the external link problem and still give you the ability to view all of the Flash graphics. With the ever-changing internet, some links will go dead. If a link no longer works, you can generally use a search engine to find the information you need. Internal File Manager Links: One advantage of Safari is that, when you click on a link to a Windows folder/directory, it opens the Windows file manager. This means, if you have an image viewer that allows you to scroll through images with a click or roll of the mouse scroll wheel, you can do so (IrfanView, highly recommended). Safari will also generally open files in their native/default application (important for .PDF files), instead of opening them in the browser's internal PDF reader, as Chromium portable does. As far as I can tell, no version of Chrome will use the native applications. For graphics, every image is a separate link that you have to click. If you open the Windows file manager (Windows Explorer, File Explorer) directly and copy/paste the link into the address field at the top of the file manager and hit return/enter. This will bring up the folder and allow normal file interactions. More on this, below. Navigating directly to file locations is much quicker if you have the Everything Search Engine installed. Drop a folder or file name (not the complete file link) into its address field and it immediately comes up. It works especially well if you can only remember part of the file name. Start typing and the possible file names start to come up. The more you type, the shorter the list becomes. When you see the file that you want, you have a couple of options. Either double-click to open the file or right-click it and select 'open path' to open the folder with the file you searched for. To test this, open Everything and start typing *500a2* or *200ix* in the Everything address field. The most efficient way to search is to type two asterisks and then start typing between them. You will see that it makes it very easy to find files, by name. Bear in mind that it doesn't search contents of files which will generally make it much quicker than the native Windows search. The Windows Key: By using the 'Windows' key + e, you will be able to open the file manager, directly. You will see the following block of instructions (or a 'navigate' link back to here) in various parts of the tutorial. This helps you navigate much more efficiently. This is the link to the MiscellaneousStuff folder. Click the link above if you're using Safari (preferred browser for opening files and folders). If you're using Chromium Portable, copy the link address (right-click link and select copy link address) and drop into the address field of Windows Explorer. Using the Windows key + E will open the Windows Explorer file manager. ^^^ Try this now ^^^ with both the Safari AND Chromium Portable browsers Notes/Review: There may be instances (in some browsers) where you may not be able to enter values into the Flash graphic text fields if you try to enter them where the graphic resides on the page. If that happens, click the link below the graphic to open it in its own tab. This should resolve the problem. If not, email me. THIS is what you will see if browsing files/folders with Chromium. THIS is what you'll get when browsing the same files/folders with Safari. Safari won't work for most external links. Use Chromium or, when Chromium portable won't work with the external links, copy and paste the link into your preferred online browser. You won't miss much, externally. Most are links to McMaster. For most links in the tutorial, Safari is far better than anything else. When you go to paste the copied address into the address field of Windows Explorer, the word 'computer' will be there. Click on a vacant part of the address field and the background for 'computer' will switch from white to the default system color (generally blue). At that point, you can right-click in that field and paste the address. Then hit the 'enter' key to go to the folder with the files for that link. ^^ Will work for copied/pasted addresses that have the full file link (like the one below, small text so it would fit on one line) and will open folders in Windows Explorer. It will generally open files in their native viewers (good for PDF files). You can copy the text below and try it in Windows Explorer. Use the Windows key + E to open it as suggested above. file:///C:/power%20supply%20tutorial/power%20supply%20tutorial/repair_tutorial/miscellaneousstuff/jbl/bp1200p1_sm.pdf For partial names, use the Everything search engine (if you have it installed) and the asterisks (for more thorough searching) from inside the repair tutorial folder. When you right-click, THIS is what you'll see. Choose the Search Everything option and search as suggested. The various links in the tutorial are generally set up to open in a new tab. If you click the links (as you should), you can have too many open tabs if you don't immediately close them. If you find one that you want to keep open but want to close the rest, right-click that tab and select 'close other tabs'. That will leave you with only the selected tab open. To keep more than one open, slide all the tabs you want to keep open to the left. Then use the option to 'close tabs to the right' (not an option in Safari). CTRL-F: Many keyboard shortcuts perform the tasks immediately but some like control-f require input. Control-f is 'find'. It brings up a dialog box or text input field and allows you to enter a word or string of text when you hold down the control key and while it's down, you press the F key. This works universally on virtually every Windows application. The Windows 'find' function is very thorough and therefore can take a relatively long time to complete a search. The wider the search field (the entire computer), the longer the search time. Searches of relatively small volumes, like the tutorial, don't take long... AFTER Windows has indexed the files. It does this, generally, when your computer is otherwise inactive. The 'Everything' search engine recommended on the TT10 page (and above - it's wonderful software), item #22. The Everything search engine only searches file names but if you know the file name or any part of it, the returned file list is almost instantaneous. As an example, I searched the tutorial for 500m (an amp model) with both the Windows SE and the Everything SE. Windows returned 85 items. Everything, only one (which happened to be the one I needed). Try it for yourself if you installed Everything.

I Component Part Numbers

Throughout the tutorial, you will see various part numbers for various components. The semiconductors that are available from the various manufacturers are not available forever. Some are available for only about a year. Some for 20 years or more. There is no way to avoid using part numbers and there is no way to suggest replacements that will be available forever. Although the semiconductors are the biggest problem, this applies to various other components as well. Keep this in mind when you come across obsolete part numbers. The part numbers used as examples were the ones available at the time that that part of the tutorial was written. In some instances (the output transistors in class D amplifiers, especially) replacement semiconductors that are compatible with the circuit may be difficult to find. To find working/suitable replacements, it may take a bit of comparison of specifications and then extensive testing, trial and error. Some class D circuits may require a bit of re-design to get them reliably repaired. Keep this in mind when you find that an amp uses obsolete transistors when you give a quote to repair the amp.

J Radio Shack References

There are quite a few references to Radio Shack items. At this time, RS is still in business and still has some stores open. Even if Radio Shack disappears, some of the items mentioned in this tutorial will be available on eBay. As a side note (and possibly only of interest to those who grew up with Radio Shack catalogs) there is a great site that has old Radio Shack catalogs that you can browse. When you need a break from the tutorial, visit the SITE. if you're using a browser that won't work with the link: http://www.radioshackcatalogs.com/catalog_directory.html

K Another of the Easter Eggs

For those who read the information in the yellow table above (again, that information is VERY important)... If/when you visit this page again, you can skip the content in the yellow table by clicking the 'Introduction to Car Audio Amplifier Repair' line of text above the yellow table. If you used ctrl-mouse scroll wheel to resize this page, remember that you reset the zoom with ctrl-0.

Getting the bad news out of the way, first... One aspect that makes doing this work more difficult is a lack of technical documents (service manuals, schematic diagrams, revisions, test procedures...). Do not expect any support from the manufacturer. It's rare. Some go as far as to deface parts to make it more difficult to repair the amp. This is especially true for the Brazilian types of amps (some are from Brazilian manufacturers and some are Chinese knock-offs). If you're in this for profit (<< not a dirty word) and won't see many of the amps for which you have no support from the manufacturer and that have defaced components (especially the output transistors), PUNT. Let the owner send it to the manufacturer for repair. Don't let them make their problem your problem. If you want to experiment with repairing an amp using parts that you believe will be reliable replacements, only risk this if you know the owner VERY well. Experimentation is a much better choice if you're working on amplifiers that you purchased to 'practice' on. Be aware that, just because the amp works for a short while in your shop, that doesn't mean it will be reliable long term.† If it fails, prepare to be married to it. If you're struggling to survive and you have the chance to repair a problem amp like this, don't. It could get costly (both time and money) and you don't need that if circumstances are already difficult. Executive decisions like the one above will come up repeatedly. Make the ones that are best for you. There's nothing that says you have to repair EVERYthing that comes into your shop. I did this when I was first starting out... don't. †Properly repairing some amplifiers can be time consuming and to properly repair an amplifier means that all aspects of the repair are addressed. This includes properly adjusting the protection circuit components for some amplifiers (many of the Brazilian and Chinese amplifiers that have defaced parts). To get an idea of what's involved with a proper repair on those amplifiers read THIS page. The process is not trivial.

• Technical Documents were mentioned above. There are a few exceptions to the problem of no technical documents being available.
• It's generally easy (not always free) to get schematic diagrams in service manuals for Japanese equipment and bare diagrams (no part lists or other information) for older Rockford amps. For many others, you have to be satisfied with 'close enough'. Fortunately, there are MANY clone type amps so it's often possible to get a schematic diagram that is usable.
• Email me if you can't find the diagram you need on any of the sites on the TT4 page, item #7. Pay special attention to ElektroTanya in that section. Be aware that it will generally block any browsers that use adblockers. As of now, the Brave browser (which uses adblockers) can still download.
  babin_perry@yahoo.com
• Another technical document is one of your best friends in repair work... The datasheet. This document is published by the manufacturer and is produced for virtually every electronic component that has a part number in any amplifier. There are 800+ datasheets included in the Semiconductor Datasheets folder† of the tutorial. There will be links to most of these, as needed, when those components are introduced throughout the tutorial.
• Many of the various ICs have alternate part numbers for ICs that are very nearly identical but have slightly different specifications. The difference in the part number is generally in the first digit after the letters in the part number, as in TLX94 (<<< the X). This applies to many of the ICs. The datasheets are often listed with one of the less common numbers. For example, the LM293 (a common part number) is on the LM393 datasheet. There is no LM293 datasheet.
  If you install and use the Everything Search Engine, you right-click and choose search Everything from the dialog box, then enter [space]LM[space]93 after the long default file address. The same works for the LM361 ([space]LM[space]61) and others. The standard Windows search engine will often work if you search for a part number but if you're searching for something that's found in many other datasheets (like 1N4148), all of those will also be returned. The Windows search engine will sometimes be preferred for times when part number might not only have one digit different. For example, the 1N5231 (which is in the zener diode 1N5221B-D datasheet). Try both options.
  For no other reason than... Why not?
  If you sit at your bench (or wherever your computer is located, workbench preferred) to eat lunch (or possibly all meals, if you're like some techs), open the datasheets folder and click on random datasheets, just to get a bit more familiar with what they include and how similar components have specific types of information.
  †If you aren't using Safari and didn't read the yellow section at the top of the page, click HERE to learn how to properly access the datasheets folder with the Windows file manager.

For most all conversations related to the repair of the amplifier, it's best to have documentation. This is generally best done via text/email (email preferred) so that there is a clear record of the discussion and agreements as to the work expected, prices, warranty... This protects both you and the customer. When contacting the customer, it's important to have one long email thread. This will make it less likely that fragmented messages will get lost. In all replies, let the previous email remain inline. This makes multiple copies of all messages in both the incoming and outgoing emails. You may think that you missed nothing when you did the initial troubleshooting but initial troubleshooting can't generally find all faults and most definitely can't locate parts that are weak (fail unexpectedly during testing). Any time that you encounter a problem that could lead to a dispute, clear it up with the owner before you do anything more. It takes just a few minutes to send an email and costs nothing. After you get more experienced, you can adjust the policies regarding this to best suit your needs. This will be mentioned again but you need to be aware that some customers will not pay for an amp that's not repaired up to their expectations. Some will expect a 20 year old amp to be 100% as when new (mechanically, as well as electronically). Through conversations, you can help determine what they expect. If the owner seems dodgy, punt! Just tell them you can't repair it. Do NOT tell them that you can't get the parts because some will want the part numbers and will try to get the parts themselves. The right price for services sometimes comes up and there is no universally correct number. Factors such as overhead, the amount of work available and the market you're in will all make a big difference. Quotes and initial troubleshooting are covered, in more detail later on this page. On the TT2 page, item #13 has more information on giving quotes. The term 'short' or 'short-circuit' is going to repeatedly be used so we need to define it. Terms/components in the following graphic may not be familiar but what's important are the general concepts. The term 'short-circuit' (often reduced to 'short') simply means that, in some electrical circuit, the current is flowing through a shortened path (not flowing through the entire circuit that it's intended to be flowing through). When this happens, the most common effect is excessive current flow which often overloads components and causes various failures. A short can be due to a component failing (like those represented above) or by something bridging circuit points. One example of this could be the primary windings of a transformer shorting to the secondary windings of the transformer when they should be isolated from each other. There have been many times where wire strands (from people stripping wire near the amp)† have shorted components in an amplifier. Other times the short can be from a technician allowing their meter or scope probe to slip and bridge adjacent component terminals. Many of the ICs operating at relatively high voltages, like the audio driver ICs in class D amplifiers, have virtually no chance of surviving an accidental short between terminals. This why it's important to keep your meter probes sharp. †This is a significant problem where finely stranded wire is used. It's nearly impossible to strip it without losing a few strands. Too many people strip wires directly over the amplifiers. Even if it's stripped near the amplifier, strands can get into the carpet and work their way into the amplifier. If you see strands of wire in an amplifier, explain what has happened, what to avoid doing in the future... and tell them to carefully vacuum the carpet in the vehicle to remove all stray strands of wire. When you find an OEM service manual or schematic diagram that exactly matches the make/model of the amplifier you're servicing, don't assume that it will be 100% accurate. There are mistakes, revision changes, engineering drawings that were never supposed to be released, part obsolescence... You will rarely find a 100% perfect match for the amp you have. Use common sense, look at the circuit design and try to determine why there is a difference. If the part looks original (section on that upcoming), leave it as-is unless you have a very good reason to change/replace it. If you have assets (home, cars, savings...) and want to protect them against possible lawsuits, you may want to form a company (either LLC or become incorporated). What I know about either could be written legibly on the head of a straight pin with a broad tip felt marker. There is plenty of information about this online. Use your preferred, modern browser. This is a topic that could be used by malicious sites to steal personal information and you want to protect yourself. And again, if you're not using a signal source with a grounded shield (remember, only $10 in parts) and an intermittently shorted transformer causes a car fire (that could be parked in an attached garage), you'd better hope your A is well C'd by insurance and/or LLC protection. If you're going to disassemble an amplifier, be warned that opening many amplifiers will void the warranty. If the amplifier is severely damaged, breaking the warranty stickers/seals may well cost the owner of the amplifier hundreds of dollars if it has to be sent back to the manufacturer (you'll be at their mercy). You first want to check to see if the amplifier actually has a problem. Many times, the problem is in the vehicle and the amplifier is just fine. BEFORE opening the amplifier, ask the owner if it's under warranty. If it is, inform them that the warranty will be void if you open it. If it's supposed to be under warranty and the tamper-evident label/sticker is already broken, immediately show the owner so he knows that you didn't break the seal. This is only one advantage to talking with the owner when he is there to drop off the amp. Avoid problems before they become problems. If you take in repairs via shipping/mail, include this type of information on the site so that your customers know what to expect. THIS is a link to a sample of what I used to have when I was taking in repairs. I'm sure that all of the forms are well out of date (some of this is from about 2009) but it may give you some ideas of what to include. It seems that everyone wants to get more power out of their amps. This tutorial only includes modifications that resolve design flaws. There is no magic bullet when it comes to getting more power out of an amp. You have to change virtually everything to get any useful gains and even then, the heatsink may not allow anything more than short bursts at the higher power because it can't soak enough heat from the transistors.† Using replacement transistors that are rated for higher power won't generally do anything to boost power output and may cause more problems that could require a re-engineering of the circuit. †The term transistor has been used but hasn't had a detailed description as of yet. That will come in time, but will have to be introduced in steps because there is no simple, comprehensive way to cover them. For now, understand that the transistors are the majority of the electronic devices that are tightly clamped to the heatsink and are the workhorses in an amplifier. They do virtually all of the hard work, pass all of the high-current and dissipate the most heat of any of the components in the amplifier. Below, the transistors are in the yellow rectangles. Of the other four devices clamped to the heatsink, two are voltage regulators and two are rectifiers.

...perfectly good semiconductors (transistors, rectifiers, regulators...) if the amplifier is powered up without having the semiconductors clamped tightly to the heatsink. Even with no speakers connected and no audio signal, an amplifier can fail catastrophically within seconds if the components that are normally heatsink mounted are not being cooled by the heatsink. This will be repeated elsewhere but this is VERY important and it's common to create MANY other problems because a component failed due to it overheating. This is a simple mistake that can be costly in replacement parts and labor (troubleshooting plus the time to replace the defective components). For those into sports, this would be considered an unforced error that cost the team the game. One case in point... I was working on an MTX amplifier and had removed the clamps from some of the components. I powered up the amplifier for a few seconds and a regulator transistor overheated and shorted. This happened very quickly. When the transistor shorted, it destroyed (explosively) several SMD (surface mount device) capacitors, both fans, several SMD semiconductors and several SMD resistors. If it's not possible to work on a particular problem/fault with the amplifier in it's original heatsink, you can use a makeshift temporary heatsink that will keep the components relatively cool (at low power/idle). Summing up the previous 2 paragraphs, take your time, pay attention to the temperature of components and follow suggestions offered in the tutorial. Keeping components clamped to the heatsink when testing is one of the most important. It may be time consuming but when you first start this type of work, simple mistakes can cause you to get discouraged. Don't let avoidable mistakes derail you. Above, the term 'heatsink' was used. Many times, the term is shortened to 'sink' when referring to the heatsink. Do NOT use 'sync' as an abbreviated form of sink. It's an abbreviated form of synchronize. Those who are educated/experienced will consider you to be un-educated or worse, an idiot. When asking for help, many of those who are trying to help will not help anyone who they feel are too stupid to warrant their time. I will generally try to correct those using incorrect terms (until it becomes obvious that someone is too lazy to try to make an effort to educate themselves). That said, I will refuse to help those who won't, at least, try to write properly (punctuation, capitalization, spelling). Until you know an amplifier well, you should always have the semiconductors clamped to the sink when the amplifier is powered up and you should have either a current limiter or a relatively low-rated fuse (10-15 amp) in series with the B+ line. Having the semiconductors clamped to the sink keeps them from overheating. The low-rated fuse in the B+ line helps prevent excessive current flow if something is significantly wrong with the amp. Later, you'll see how low value resistors (in place of the low-rated fuse) are used to allow the amp to power up while preventing excessive current flow. I use ATC/ATO fuses when I need to protect an amp with a fuse. ATM and ATM-LP may also be OK choices since they're very similar to the ATx fuses. Fuses like 5x20mm or AGC fuses may blow more easily than the ATx fuses, are more difficult to find and may not be, in any way, a good choice. Fuses like the MAXI or AGU of the same rating as the ATx fuses will typically take longer to blow and are much more expensive than the ATx fuses. If you stock them as replacements for blown/missing fuses in amplifiers, you can use them but go to the next lower fuse value than you'd use with the ATx fuses. THIS is a link to the Fuses page where you will find more information on all of these fuses, alternative fuses and fuse holders.

• Are the parts in the amp original or not?
  If you don't know if the installed parts are original, there are several characteristics to look for.
• The first is to see if they're all installed perfectly perpendicular/square to the board and at the same height. The manufacturers use jigs and/or robots to position parts. It's difficult to get the same consistent positioning when repairing an amp.
• The second is the solder joints. The OEM flow soldered connections will be dull and again, very consistent. If the connections are shiny and/or have varying amounts of solder, be suspicious that they may not be original.
• Since most techs fail to clean the flux (from the flux-core solder) from the boards, that may be one more way to determine if the connections have been soldered by hand. THIS is an example of hand and flow soldered connections. The transistor on the extreme left has been flow soldered. Flow soldering typically has less solder and has a slightly concave shape. Hand soldered connections are typically more convex in shape and often have un-cleaned flux. Although unintended, examples of these can be seen in the Orion amp photos (red board) below.
• If soft insulators are used, are there multiple impressions for one transistor location. Unless someone has tampered with the amp, there should be only one impression on the insulators.
• Are the leads bent uniformly? This is something that most repair techs fail to do, so if the leads are not all bent precisely the same, they may not be original.
• There will be amps that have modifications and you may wonder if those are OEM or if someone has tampered with the circuit. There are a couple of characteristics that may help you decide who made the mods.
  Flow/hand soldering appearance was covered and is, again, a good indicator. Another is the appearance of the components used. Manufacturers, for their modifications, typically use the same types of components that were used on the rest of the board (especially if the mods were made at the time of production). Techs may (not very likely) have components that are identical but are more likely to use components that vary, in general appearance. In the following two images, you see two mods that were OEM.
  
  
  In this image, both the solder and the components tend to indicate that this is OEM. The resistors are not all of the same profile but if you could see the same value resistors on the rest of the board, you would see that they're the same.
  The flow-solder on the board-end of the diode tends to indicate that this is also OEM. The via where the diode would have been soldered into the board also has the appearance of flow soldering. In comparison, the different appearance of the resistor, positioning, solder and flux tend to indicate that R85(?) is not OEM.
  
  
  Appearance of the part alone isn't always enough to decide OEM or not. The resistor below is OEM and is one of a relatively small number of resistors (output base resistors and a few others) of this style on the board. Everything else about it, however, says it's OEM.
  
  This (R210 below) is obviously not OEM. This shows shoddy work (it doesn't get much worse), using two series-connected resistors as a single resistor. Using series/parallel connected resistors is a viable (temporary) solution that can be used to make resistor values that you don't have in stock and will have to order. Doing this to allow further testing saves time and shipping but should not be used in amps you're being paid to repair or may sell in the future.
  
• The photos above were taken before repairing the amp (so... not my work).

This can make the difference between success and failure. Well taken notes let you to make a reference for yourself that you may not be able to get from any other source. Follow the links for note taking each time you see them. Good records and reference information can make the difference between making money or losing money for many repairs. In addition to taking photos, record various characteristics like the idle current. This isn't, necessarily, just for an amp you're repairing. This can be taken from amps known to be in good working condition (you'll be asked to bench-test amps to see if they're working before being installed by a car audio shop. Having this information (and any other information that you record) can help determine if there is a problem with the various drive circuits. This may or not be viable for everyone reading this but most cell phones can convert voice to text. If you don't want to take the time to write anything down, use the voice to text feature on your phone and send the text messages to your computer. Then move them to the appropriate folder on your computer. Don't store everything on your phone. They get lost or stolen and you don't want to lose (possibly) years worth of valuable data. On many amps, there is an initial idle current (power supply operating only) then a jump in idle current as the bias circuit is engaged (class B, AB... amps, can commonly be seen in Rockford amps). For switching amps (class D...), when the output stage is enabled (the output transistors begin driving a square wave rail-rail), there is also an increase in idle current. You'll see more encouragements and suggestions for taking notes throughout the tutorial. It may also be helpful to note if any components operate at high temperatures. Large resistors will almost always run hot at idle (not referring to the emitter/source resistors which are large but almost always run cool at idle). Inductors will run hot in some (most) amps. In many amps, they idle at such high temperatures that you cannot hold your finger on them for more than a second (unless you're a welder, by trade). The components that you're most likely to note are integrated circuits running hot.

• For more information on taking notes, refer to the following pages:
• Checking Semiconductors page
• Equipment page
• Repair Introduction page (different sections) HERE and HERE

Amps that fix themselves are just as likely to UN-fix themselves. If you receive an amp for repair that has a problem and the problem miraculously resolves itself, do NOT consider that amp repaired. Intermittent problems are common. Many times, there will be an intermittent short or an intermittently open connection that will temporarily disappear and no matter how you stress the board (flexing/tapping..), you won't be able to make the fault return. If you charge owner for repairing the amp, EXPECT the amp to come back. If you tell the owner that the problem is intermittent and that you're not 100% sure that you found it, it will be better than if you tell him it's definitively repaired. If you let customers know that there may be a problem and that you'll cover it (repair it for no additional charge), they're more likely to be understanding. You should, however, explain to them that you will not cover additional damage if the amp is improperly installed. The alternative to this (and better in my opinion) is not to charge for the repair. When you do something that should not solve a problem and it does (replacing parts that checked OK after you removed them), you should suspect that it's a coincidence and something else changed as well. While the amp is powering up normally, twist/push/pull on the transformer and inductor (if it has one) to see if the current draw changes. Shorted transformers and inductors can (and do) cause intermittent problems. Windings can short to other windings, to the circuit board and to adjacent components. When stressing the transformer, it's best to power the amp up through a current limiter. For amps that won't power up through a current limiter, use a low-rated fuse. A 7.5 amp fuse will typically work for small amps. Except for really high powered amps, you shouldn't need more than a 15 or 20 amp fuse. Use the lowest value that you can to offer the best protection for the power supply FETs. As a side note, one problem with using current limiters (which are very useful) is that some amps will never power up from a power supply that has current limiting below about 15 amps. There have been requests for help from too many people using a 3 or 5 amp supply that have wasted many hours troubleshooting a problem that didn't exist. Item #6 on the Equipment page has more on using a current limiter.

When repairing amplifiers, and more specifically older/vintage amplifiers, you need to determine if the owner is a 'collector' or someone who simply likes older amplifiers. The two are very different. A collector will likely know every scratch/dent/ding on the amp. They may even be aware of all minor defects on the inside of the amp. While you always want to take care not to do any damage to an amplifier, you have to be especially careful with amplifiers for amp collectors. Sometimes, when repairing an amp, you may allow the barrel of the soldering iron touch a wire or some other component with a relatively low melting point (like the plastic casing for the capacitor below). For a standard repair, this may be absolutely insignificant but if it happens when working on a collectable amp, it could be a significant mistake. Part of the value of the amp may be that all of the wiring is original and in perfect condition. If you accidentally melt one of the wires (striped wire used in vintage Orion amps) and an exact replacement isn't available (short of buying an identical amp to salvage the damaged parts from), you may have problems when the owner comes to pick it up. Something else that you need to discuss with collectors is the level of repair. Do they want you to undo all previous repairs that don't look original. This could include replacing resistors that are not the same size or physical appearance of the original parts. You also need to determine if they want a repair or a complete refurb. A repair would get it back to good working order. A refurbishment may include replacement of ALL of the electrolytic capacitors and ALL of the heatsink mounted semiconductors. A complete refurbishment may take a full day or more where a repair may only take an hour or so. You need to know what they expect to quote the price accurately. Some of the older, valuable, collector's item types of amps had knobs that could be (accidentally) pushed back into the face of the amp, breaking the potentiometers. Since these old potentiometers are well out of production and virtually impossible to find (if they need to be replaced), it's imperative that you not break them. Below, one knob has a shoulder and the other does not. The ones without the shoulder are the type that can cause problems. When you get an amp that could have an issue with the knobs breaking the potentiometers, remove the knobs immediately and keep them attached to the bottom cover or heatsink of the amp.† The knobs are nearly as hard to find as the pots so you do NOT want to lose them. †Do not use tape to attach the knobs to outside of the bottom cover. The paint is often on the verge of peeling off and tape can pull it off. Even the blue painter's masking tape will stick aggressively if left in place for a long period of time. If this is for a collector, he will NOT be amused if the paint and/or markings are damaged. Put the knobs/accessories in a Ziploc type bag and use a piece of string/wire/zip-tie to attach the bag to one of the mounting holes in the cover or to a screw that's screwed into the end of the heatsink all but about 1/8". If a significant length of screw extends from the heatsink, it could easily be broken off and could be difficult to remove. If the amp has to be shipped back to the owner, protect the knobs or leave them in the bag and let the owner reinstall them. If you don't keep the knobs (or any accessories) attached to the amp, make a note (that cannot be lost) of the 'safe place' where you put them and what the container looks like. I've put hundreds of items in a safe place... and forgot what/where that safe place was. With my luck, when I finally find that place, I'll also find Jimmy Hoffa. Everyone knows that parts can be printed in 3D but, for the most part, the parts are not printed with a perfectly smooth finish if printed by a desktop printer. Higher quality parts can be produced but it typically takes a much more sophisticated print process. This can be done by internet printers (in either plastic or metal). The replacement parts will have to either be modeled by you or scanned into the computer by a laser scanner. This is doable but can be expensive.

• Selling Amplifiers:
  There are several possible issues that you should think about if you intend to sell amplifiers.
• If you ever intend on selling old amps, you should know that some collectors (likely the buyers for vintage amps) may want them original (no mods, no repairs). Many collectors have learned to repair the amps they collect and would prefer to have an amp that has not been tampered with. Doing anything to the amps could reduce their value. You shouldn't even replace the capacitors. Not all caps fail. If there are caps leaking electrolyte (which can destroy a circuit board), those need to be removed or replaced but many do not. You should also know that some caps are very difficult to remove without damaging the board. If you have/own a collectible amplifier that you intend to sell, don't do anything to it (with the exception of removing leaking capacitors and cleaning up the electrolyte) until you find a buyer and ask the buyer what he/she wants.
• There are different types of repairs for amplifiers, like there are for cars or virtually anything else. The repair that you do on your own 'stuff' (to cover as much as possible) may vary from what you do when someone is paying you to work for them. As an example, I've seen techs cut the legs from one shorted output transistor and solder a used transistor to those legs (never removing the board) and let the amp go like that (for a paying customer). That's wrong (in my opinion). If you're repairing an amplifier for yourself for something to use in your workshop and you do that, that's fine but if you intend to sell the amp to someone, do the repair properly. The exception is if you're going to give them the amplifier (no cost). As you read along, you'll see the right ways to do repairs. If someone is paying you to do a job, charge a fair price and do the job properly. Have pride in your work.
• This will be mentioned again but... If you have any other techs in your service area, they will likely try to take business from you. They can easily do that if you do poor quality work. Remember, I'm pullin' for you... Hmmm... had a Red Green flashback there.

You did read EVERYTHING in the yellow table at the top of the page, didn't you? If not, you WILL miss out on some of the features and content. It will take just a minute or two to read it. For example, what do you do when you click on a link and the landing point on that page isn't what you expected? Generally, people close the new tab/window and let themselves believe that clicking the link was pointless or a mistake. A mistake, possible (some links are broken because content was moved to a more appropriate location), but done for no reason, not likely. If you find such a link, email me. Although some people are better at this type of work than others, virtually anyone can learn to do repair work. If you have no experience with this type of work, when you open the first amplifier, it will look completely foreign to you. It's unlikely that you'll know what any of the parts are and if you know what they are, it's unlikely that you'll know what they do. That's to be expected. Although there is a lot to learn, it's really not too difficult. If you don't remember/absorb everything the first time you read it, it may be discouraging but that's also to be expected. Each time you read through it, you'll pick up more and more information. If you perform a few repairs and re-read part of the tutorial, more points/concepts will begin to make sense. Keep in mind that this tutorial contains VERY little irrelevant information. Virtually everything here is important. I'll suggest that you read through the entire tutorial once BEFORE you attempt the first repair. This will let you know precisely what information is provided. Then, when you begin to work on the first few pieces, you can refer back to the relevant sections. If you read this page carefully and follow the links provided, it should take you at least several hours to cover this information. If you want to run through it quickly and then, at a later time return and read it thoroughly, thats OK. If you're new to electronics and repair work, I strongly recommend that you take your time. When initially troubleshooting, you will often do the absolute minimum to get the amp to function at the most basic level. This allows you to determine the severity of damage to the amplifier. When doing this, you will often use as many of the original parts as possible, generally removing only the ones that are preventing the amplifier from functioning and replacing a minimum number of parts to get the amp up and running. When doing this, it's common practice to use parts that survived from other repairs (that had to be replaced so you could have matching parts† in the final repair of a previous amplifier). This is covered in a bit more detail on the Class D - Type 1 page. Read THIS section (in the cordoned area) and return. There is much you need to know before you can understand what's on the rest of that page. †This will be repeated throughout the tutorial but you will have instances where you have parallel components that have to share the load equally. This is where you need components that have matched characteristics. You won't typically need to do anything more than to use components that are from the same production batch (have matching date codes). There will be times where you find a significant number of defective parts and install their replacements and the amp won't power up. Too many people just start pulling all of the new parts to recheck various components/circuits (possibly some that were dismissed as OK, previously). If this happens, try to find a way to disable various sections of the amp to see if you can get the amp to power up, in part, without having to waste hours removing parts, clearing vias and reinstalling parts. Email me if you need help with this sort of problem. To expand a bit on the statement above... Too many people, for some unknown reason, feel the need to remove all of the power semiconductors (those clamped to the heatsink) to check them. For virtually 100% of the times when an FET fails, it will be obvious in the board (0 ohms between at least two of their terminals).† It's possible/common for all of the power supply FETs to fail but, except for very large amplifiers with large capacitor banks, output FETs typically only fail one or two at a time. Check them in the board and when you find one that has suspect readings, pull it alone. If you have questions (before you waste time pulling a dozen or more FETs), email me. †Some of the items in the next diagram will be unfamiliar but you can understand the basics. The center-tapped rectifiers (like the MUR1620CT) will appear to be shorted between their outer terminals. That's the transformer that's making them look shorted. The fine white line shows the current path that your meter reads when checking the diodes in the circuit. If the center-tapped rectifiers are not reading 0 ohms to the center terminal, there is no need to pull them for checking out of the circuit. I know you won't like this but... If you're like virtually every other person who has learned to do this type of work, you will make mistakes. Repeat, YOU WILL MAKE MISTAKES. You WILL short out components with your meter probes. You WILL install parts the wrong way (backwards). You WILL remove parts and forget where they go. All of these mistakes will lead to the destruction of parts and will be a gut-punch to your ego. It's not the end of the world when you make a mistake (but it will be annoying). When parts start to fail in a dramatic way (smoke, fire, tiny explosions), DON'T panic. Calmly remove power from the amplifier and assess the damage. If someone says that they've never damaged any parts doing this type of work, you can be sure that they're either a liar or haven't done much repair work. With experience, you'll be less likely to destroy otherwise perfectly good parts. When you set up your work bench, use a quick-disconnect like the one shown under TT5, item #23. In the above demo, the current draw only becomes excessive after remote voltage is applied. This is indicative of (most commonly) shorted audio output transistors but can also be due to a shorted rectifier, transformer or maybe even stray wire strands that have fallen into the amplifier. If the amp draws excessive current before remote voltage is applied and the power wires haven't been inadvertently connected with reverse polarity (backwards), you'd immediately disconnect the amp from the power supply and pull the cover on the amp to begin troubleshooting. If an amp's power supply connections are connected with reverse polarity, it can sometimes damage internal components. If you do this and you're lucky (or have the proper protections in place on your bench), it may not do any damage and making the proper power connections will allow you to continue testing. When an amp is drawing excessive current, the power semiconductor components that are normally clamped to the heatsink can heat up very quickly and can fail within a few seconds. That's why you must carefully monitor the current draw of an amplifier if you don't know for a fact that it's in good working order. It's important that you always have the heatsink-mounted components clamped tightly to the heatsink when testing an amp if you don't know if it's working properly.† Even if it is working properly, when testing the amp at anything more than minimal power output (with all protection devices, current limiters, etc... to be shown later) in place, you should have the heatsink mounted components clamped. †It's important that you always have the heatsink-mounted components clamped tightly to the heatsink when testing an amp if you don't know if it's working properly. << I know it's odd to dagger a sentence then simply repeat it but this sentence is just that important and for those who are doing nothing but skimming this (exceedingly important) page, maybe they will read at least one iteration of the sentence. It's a bit like the repeated warnings not to buy replacement semiconductors from eBay/Amazon. In the following image, it may appear that the un-clamped transistors are against the heatsink and could transfer heat to the heatsink but that's not the case. When the clamp was removed, the transistors lifted just slightly and would overheat quickly. In a situation like this, if these transistors would fail (these are the output transistors), it would stress the power supply and could cause it the power supply FETs to fail catastrophically. In an amp like this (Power Acoustik A3000DB), this mistake could require that you replace nearly 50 parts (16 PS FETs, 16 gate resistors, 10 audio output transistors, driver transistors...). Take the time to clamp the transistors when the amp is powered up until you're experienced enough to know precisely what to expect. And... don't make the mistake of starving your amp for current.

• Notes:
• Above, it was stated that large amps could draw as much as 5 amps at idle. For some of the largest amplifiers, the idle current could be even higher. I've seen as much as 8 amps and have heard of higher idle current draw.
• To know if an amplifier is drawing excessive current at idle, you have to know what idle current is supposed to be. In some instances, the owner's manual (online search) will tell you what the idle current should be but that's not always available. It's best that when you make a folder to store the photos that you've taken of the amp's internals (you're are doing this, aren't you?... AREN'T YOU?), make a simple text file or use the templates that you will see later and store notes about the amp's repair. In that file, include the idle current measured from the amp in fully working order. Even if you don't know if the idle current is what it should be, repairing several more of the same model and including the values that are different for each will give you a relatively accurate average current draw. THIS is an example of the type of information you might include. Save it with the make/model in the file name.

I always suggest that newbies begin with the simplest of amplifiers. The simplest amplifiers are typically the budget, class B (to be covered later) Asian amplifiers (from China and Korea). They generally have simple problems and they don't destroy a significant number of parts when they fail (generally). I would strongly suggest against starting with many of the American brands (particularly those that use surface mount components). Amplifiers like those from JL, MTX and Rockford can be difficult to repair. They are very good amplifiers but are much more complex than the cheap stuff. If your first repair attempts require that you repair complex problems in complex amplifiers, you'll get discouraged and will most surely be doomed to failure as a service/repair technician. If you start with the amplifiers that I suggest, you will build your confidence and have a much better chance of succeeding in this business. Even if you are an extremely intelligent person, this still applies to you. There's no point in making this business harder than it has to be. Do you want a broad knowledge base or do you just want to thump your chest? (click). Another reason to start with small, simple amplifiers is that you will destroy far fewer parts when you make a mistake or fail to find all of the problems before you apply power to it. Replacing the damaged parts will be much less expensive and much less time consuming. For example, if you're working on a small (50Wx2) amplifier and you make a mistake, you'll likely have replace no more than 4 transistors. The total time to replace them is likely less than 5 minutes. If you make a mistake on an amplifier like a Rockford 800a2 (which has the transistors soldered to the insulators), the time to replace the parts will be closer to an hour. The parts will be more expensive and there will be many more to replace. The first image below is the type of amplifier you want to begin with (Bazooka EL1500). There are MANY different amplifiers of similar complexity that make good amplifiers on which to learn. The one after it (JL500/1) is NOT something you want as your first repair. Although the repairs on the JL can be simple, they often require significant knowledge to repair them. For example, the first amp has a single power supply that is the source of all power for the audio section. The JL has three (3) independent switching power supplies. Two are used when the amplifier is in operation. The third runs only in 'signal detect' mode. The Bazooka uses simple through-hole parts that are easy to deal with. Through-hole parts have wire terminal leads that are inserted into holes, from the top (component side) of the board. The leads are soldered on the bottom (solder side) of the board. The JL uses mostly surface mount (no wire/through-hole leads) components. Most of which are only 0.050" x 0.080". Some of the SMD resistors are only 2/3 the thickness of a US dime (0.33" vs 0.50"). If you try and fail to repair several complex amplifiers, you'll likely give up... believing that you're incapable of doing the work. If you start with appropriate amplifiers and you learn what's in this tutorial, you will VERY likely succeed. There are more photos of these amps in their respective folders in the miscellaneousstuff folder of this tutorial. If you're not using the Safari browser, click HERE† to find the best way to access that folder. If using Safari,† you can access the miscellaneousstuff folder directly/properly.

†Read down through the Notes/Review section at that link. It shows you the differences in what you see with Safari vs what you will see with other browsers. †Far too many people refuse to use the Safari browser but it's absolutely the best option for the tutorial (especially when Irfanview and PDF Xchange Viewer are installed). It opens the Windows file manager when you click on a folder link and allows easy browsing of those files. Other browsers (unless you're using an old version of Internet Explorer) just provide a page with individual links. Not all links to folders are critical information but are generally provided because they can be useful. If you're not usiung Safari because you had trouble installing it, email me. Before we get to the common components section, the concept of 'tolerances' should be mentioned. When anything technical is manufactured, whether it's a piece of machined metal, a special rubber compound or an electronic component, that component is designed to have certain specifications. Since it's essentially impossible to have all produced components absolutely, precisely the same, there will be variations. Generally, there is a range of variations (often determined by it's use in the final assembly) in the component that are acceptable for that particular component. The acceptable range of variations are referred to as tolerances. For most components, the tolerances are stated by giving the marked specification plus or minus a percent of that specification. For example, ±1% or ±5%. In electronic repair, you will replace components with equal or better tolerances of the original. Datasheets are important documents that you will use to identify various electronic components that you'll encounter. More than 800, for the most commonly used components, are included in the Semiconductor Datasheets folder. Datasheets are published by the manufacturers of the components and give virtually anything and everything you could possibly need to know about that component. They can vary from a one page document to a ridiculous 500+ page document for a microcontroller. Fortunately, most datasheets are no longer than 20 or 30 pages and the relevant information is near the top of the document, on only 3 or 4 pages. Distributors (even reputable distributors) are not infallible. There will be times when you see specifications for a component and it appears that one component (with the same essential part number, just a different prefix/suffix) has significantly different specs (current rating is commonly wrong). For those parts, open both datasheets and look carefully at the specification and all parameters. One common specification that changes is the current rating for two different temperature extremes. As an example, the continuous current rating for an FET (given in the datasheet for the IRF3205 — click to open) may be 110 amps at 25°C and only 80 amps at 100°C (virtually all electronics are derated as their temperature increases).† When the distributor was filling in values for current, one may have chosen the 25°C value and the other the 100°C value. When you open the two datasheets, you can compare the two matching specifications. †Derating is mentioned above. When looking at the various datasheets, you'll see that virtually all graphs showing the characteristics of a component are given as a curve. This is especially true for temperature-related specs. For that FET, there are notes about the silicon current capacity and the package current capacity. The silicon rating is good information for quick surges but the package has to be able to pass the current and may not be able to pass the full silicon value continuously. As a side note, the silicon value is short term only because the thermal conductivity from the silicon isn't infinite so the silicon will heat relatively quickly and lose current capacity. Comparing specs on datasheets from one specific manufacturer is an apples-to-apples proposition. It's not always so straightforward when comparing component specs from competitors. The differences in testing procedures and terminology can lead to confusion. This is to be expected and sometimes, you have to (sort of) read between the lines to understand the differences.

What immediately follows isn't intended to be an introduction to troubleshooting. It's a common scenario. Several points above mentioned measuring voltage, resistance, etc... After looking for any obvious physical damage, the first troubleshooting you'll do on an amplifier that won't power up fully is to measure voltage. Then, if voltage is missing at a certain critical point (power supply terminals of the switch-mode driver IC...), you will trace the circuit between the points where voltage is present and correct (possibly back to the B+ and remote turn-on terminals) and where the voltage is notably absent to find where it's being lost (due to an open trace, resistor, transistor...). This is still a very early point in the tutorial (only the second page in the order it's intended to be read)<Iso you haven't learned what voltages should be present at various circuit points and on the pins of the most common ICs. Not to get too far ahead of ourselves, but, in general you will start with the primary side of the power supply and the switch-mode driver IC and work from there. Without this IC functioning, the entire audio section is likely to be 100% inoperative. When measuring voltage on any circuit board, the board is going to be energized. It's best not to make contact with the live circuit. Most importantly, you want to avoid contact with high voltage present on some boards. For sensitive circuits, making physical contact with the circuit can result in changes in the circuit's operation. At the very least, the conductivity of your skin can skew readings in high-impedance circuits but that same conductivity can cause some circuits to malfunction, possibly to the point of causing component failure. In the image below, the silicone rubber pad is placed so that a right-handed person could rest their left hand while probing the circuit and writing the values down with their right hand. This is the quickest way to collect readings if you don't have anyone to write the values down for you. The silicone rubber works very well. It's non-conductive and prevents your hand from moving, unexpectedly, causing the probe to short between closely spaced pins (which can lead to catastrophic failure of the amplifier, even if using current limiting or a low-rated fuse). When checking voltage on a live circuit, having a probe slip or trying to get to difficult-to-reach points can cause headaches that you don't need. For a few tips that may be helpful, try THIS section of the Know Your Meter page. Now, back to the point of this section, collecting data. You'll find various .ods files in the tutorial. Some are templates while others include collected amplifier data. The .ods files are OpenOffice spreadsheet files with voltages for various components in an amplifier. Since there is no space for a keyboard (I don't like the pull-out keyboard trays) on my bench, I fill in the blank spreadsheet by hand (double-checking all voltages) and then either scan the paper document on a flatbed scanner or enter the values into the spreadsheet file on my computer. Whether scanned or in .ods form, there is a record of the voltages that you can use as a reference later. The image below shows the raw version. template - do not modify.ods is the blank version of the spreadsheet for OpenOffice (a free office suite) - Calc if you want to use it. After you find it, copy it to the folder for the amp you're repairing (where you stored the photos of the amp that you took, for future reference) and edit the copy. If you are capable of navigating your computer's file manager, and can go to the folder more easily, the file is in the following location:
repair_tutorial\ods template files\templates to be edited Navigating directly to files locations is much quicker if you have the Everything Search Engine installed. Drop a folder (i.e. templates to be edited from above) or file name into the address field and it immediately comes up. You'll find data like you see above helpful when you have intermittent problems. Taking the voltages when the amp is working properly AND when it's malfunctioning can help you to see what changes and can help lead you to the problem.

• For more information on taking notes, refer to the following pages:
• Checking Semiconductors page
• Equipment page
• Repair Introduction page (different sections) HERE and HERE

The board in the image above has 'through-hole' components. For those, pin 1 often has a square solder pad (zoom-in to see it). The same goes for pin 1 of many/most through-hole transistors. The IC above has a line on one end of the body. That end of the IC has the first and last pins (numbers 1 and 8 for this 8-pin DIP IC). The IC above provides both the line and a notch. Either/both are going to be found on the IC, depending on what the manufacturer chose to use. For both types of ICs, the notch in the silkscreen outline (when used) will indicate the pin-1 end of the IC. The board below mainly uses 'surface mount' or 'SMD' components. Some (none below) SMD ICs also use a line to indicate the pin-1 end of the IC, as you saw above. If you look at the ICs below, there are several that have dimples. These all tell you that that's the end with pin number 1 of the device. If you find an IC of this general configuration† that has no such mark (only text), looking at it with the text right-side-up, the bottom left pin is pin 1. †This doesn't necessarily apply to an IC with terminals around the entire perimeter or for ICs with terminals distributed in a matrix under the body. For those, look up the datasheet for the pin numbering scheme. Various manufacturers (both IC and Amplifier manufacturers) use their own ways to identify pin 1. Virtually all will have pin 1 on the left edge, bottom when the text is right-reading. Here are a few examples. This first one has the notch in the silkscreen, the cut-out notch in the molding and a dimple/indentation on pin 1 of the IC. In the silkscreen below, you see a triangle and a beveled corner used as pin 1 indictors. The IC uses a dimple. This one is of an optocoupler and they are somewhat different, for some reason. The IC itself uses a sloped front edge on the edge that has pin 1. Its silkscreen uses the notch. The second image with four 4-pin ICs (also optocouplers) have a square notch cut alond the entire front edge. The board layout uses a square pad for pin 1. These two ICs use a line to indicate the pin 1 end of the IC. The silkscreen uses a notch as well as pin numbers being printed on the board. The SIP IC here has a notch in the top of the IC that marks the pin 1 end of the IC. The PC pad is square for pin 1. In the next image, you can see that the silkscreen has an additional line that frames pin 1.

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The text in this small section applies to those who are charging for the work they do and are charging the owners of the equipment for the perfectly good parts that they're replacing. If you are just absorbing the cost of the perfectly good parts you replace or are working on your own equipment. You're cheating no one (other than yourself if you won't take the time to ask for help or read the available material). If you're proud of getting an amp working by randomly replacing perfectly good parts until you accidentally stumble upon the faulty part, you have the wrong mindset. People who work like that are incompetent "technicians" and if you charge the owner for replacing perfectly good parts, you likely fall into the category of being crooked. How would you categorize a mechanic, HVAC tech, plumber... that did the same thing to you? And, I know, there will be some reading this that do all of their own mechanic work (including complete rebuilds on race engines) and can repair anything else that they own. This won't likely apply to you. If you're intelligent enough to do all of that, learning what's in this tutorial will be no problem and you would have no reason to blindly replace perfectly good parts. Much of this is covered in detail in other parts of the tutorial. This is an introduction to the process. The following is a basic sequence of tests that you'll perform when you repair an amplifier. When you begin to do anything, act as if someone (company owner, supervisor, head technician) is looking over your shoulder and will want a logical reason for what you're doing. Would there be that logical reason for what you're doing or are you acting blindly, out of ignorance? << Before you start chewing nails and spitting out barbed wire... Ignorance is simply the lack of knowledge about some subject. Everyone is ignorant about something. Ignorance has nothing to do with intellect/intelligence. If you don't want to appear ignorant about electronics when you work with a competent tech, do the hard work to learn the trade. It's as simple as that. There have been a number of people who have asked for help with strange problems that didn't need to be problems. When performing any type of repair, you should do so in a logical, methodical way. Too many people are trying to test various points in ways that I've never even thought of doing and are sending me oddball meter readings. As a simple example, when you measure voltage, you have to place your black meter probe on some point. That will be your reference point. Before choosing that reference point, you should fully understand what you're measuring and what the proper reference for that measurement is. The proper reference point isn't always the ground terminal on the amp but it's MUCH more likely to be the reference than the B+ terminal. I don't know where people get the idea that the B+ terminal is where they should place the black meter probe... but that's what some people do. When performing repairs, you test the amp to see how it's malfunctioning, find and replace the defective components and re-test to see if all problems have been solved. A competent technician will understand the various components and will know what those components need to function properly (various voltages, etc, ground on the correct terminal[s]) and will confirm that all are present and correct. Where they are not correct, he will determine why and work logically, from there to find the fault (out_of_tolerance resistors, defective voltage regulators, open traces...). Again, far too many people refuse to take the time to learn the way that the basic power supply driver ICs (TLx94, SG352x...) function (not even on a most basic level... Oh wait!... It's all on a basic level)† and if an amp won't power up, they blindly replace a perfectly good driver IC with another perfectly good driver IC† and... it's a huge waste of time. Take the time to learn the components. If you don't, you will never be a competent technician. Before blindly replacing parts, please email me. It costs a lot less to send an email than it does to replace perfectly good parts. †These ICs can sometimes present confusing behavior but, for the most part, there are a small number of terminals that have to have supply voltage or be grounded or have various terminals below about 3.5v but there's not much more than that to understanding them... and people still replace perfectly good ICs. If you feel that the few notes here are a bit weak regarding driver ICs, you're absolutely right. There is far more on the Power Supply Troubleshooting page (approximately 15 pages on the TL494 driver IC, alone). Remember, this is still only the first technical page of the tutorial. †The replacement may not actually be perfectly good if it wasn't purchased from a reputable distributor like DigiKey, Mouser... Sources like eBay/Amazon are not good choices for buying semiconductors. There are some reputable sellers but there are also MANY sellers who are selling counterfeit or second-rate components. I know... you already have accounts set up at eBay/Amazon and it's too much trouble to sign up for a free account at distributors where competent techs buy their parts. It's likely many of you will not heed this warning until you've spent days/weeks fighting a repair, only to find that the bargains that you found on eBay/Amazon are junk. eBay and Amazon are perfectly fine if you need a new fishing hat, semiconductors...NO! Also, expect to have unreliable/misleading readings from cheap multimeters. In a later chapter 'Know Your Meter', you will see examples of this. Many cheap meters have lots of features but have circuits that produce readings on what the meter 'thinks' it's seeing. A more expensive, complex meter will have more sophisticated circuits and firmware and can produce reliable readings. Now, I don't expect a hobbyist to go out and spend $400 on a new multimeter but if you're using a cheap meter that appears to have all of the features and capabilities of a more expensive meter, don't expect the same reliable readings of the more expensive meter. You should also know that there are relatively inexpensive meters (like the Fluke models 10, 11 and 12 — will be seen on the equipment page) that are often better suited for troubleshooting than an expensive meter. I'm no elitist. For general repair work. My meter of choice is a Fluke 10, 11 or 12. I understand that not everyone has access to the perfect equipment. This is one reason that so many alternative methods/suggestions are given through the tutorial. If all you have available is a meter that is less than ideal, at the very least, test it extensively to find it's faults and use it within those limitations. Many times, the owner will assume that a red LED means that the amp is in protect mode. Some amps (many Kenwood amps and others) use a red LED for the power LED. For many of those Kenwood amps, there is no protection LED. If the amp is in protect, the red LED won't turn on. For those who never really paid attention, a red power LED can be confusing, especially if the system has a problem, like one speaker not playing. If the owner calls before dropping the amp off to you, you may be able to ask a few questions and resolve the issues he's having without having to stop work to check out his amp. If you can get him to email you, that can be even more productive in many cases. Email is good because you can give him a list of points to check and he'll have all of them in writing.† If you give him a list on the phone, you can be sure that he'll forget at least some of what he needs to check. If you're busy, tell him that you charge $20 (or whatever you choose) to check out an amp but will help via email for free. †While not absolutely necessary, it's often good to number each question you ask and then leave a blank line (to set off each question) between that numbered question and the next numbered question. Then, if they don't answer one of the questions (the fourth question), all you have to type is #4?. Above, the red LED in a Kenwood was mentioned. These LEDs typically (always?) have a red lens. A red lens means that the LED will be only red and can't be a multi-color LED (the type often used for both power-on and protection). LEDs with a clear lens could be any color, even multi-color. It's common for a 2-color LED to be used as 3 color LEDs by lighting the two main colors at the same time to make the third color (red and green lit together make orange, approximately). When marking receipts, invoices, repair tickets..., there are a few terms that may make it look a bit more professional than writing P.o.S. on it. A price quote for a repair is 'approved' or 'declined' by the owner. If the amp isn't worth repairing, the term 'uneconmical to repair' (UTR, shorthand) is commonly used. You need to know that many (most) 12v power supplies (the ones used to convert AC mains voltage to 12v DC) have built-in protection circuits. When an overload is detected on the power supply, the power supply will shut down the output and the voltage will drop to a couple of volts or less (to 0v if the protection is provided by a circuit breaker). If it's an automatic protection circuit, the voltage will go back to 12v when the overload is cleared. I prefer the simple current limiting resistor but if you won't use one and rely on the current limiting or over-current protection of the power supply, get to understand how it works so it doesn't confuse you when the amp draws significant current. Amplifiers without a softstart circuit will have a significant inrush as the rail caps are charged. This is normal operation for many amps. This happens a lot so it bears mentioning. Some people are so afraid of damaging parts that they limit the current too much on their power supplies, starving the amplifier for current. In MANY cases, this causes the low-voltage protection to prevent the amp from powering up. The problem becomes a low-voltage problem because when a 12v power supply limits the available current, the output voltage drops (the same as with a series current limiting resistor, but not always as predictable as using the resistor). Even if the amp doesn't have a dedicated low-voltage protection circuit, the driver ICs have a minimum voltage requirement. If an amp won't power up, allow more current while very carefully watching the current draw and the temperature of the heatsink-mounted components (if they're not tightly clamped to the heatsink). If it attempts to power up, but won't and any components are getting hot, that can quickly lead you to the fault and is much better than wasting hours due to excessive current limiting. As an alternative to current limiting, use a 10-15 amp ATC/ATO fuse and clamp all semiconductors down tightly to the heatsink as was suggested above. For more on current-starving an amplifier, click HERE.

• Initial Inspection to Determine Amplifiers Condition
  Smoke Saves Time:
  Of course, if the amp still has smoke pouring out of it or smells like it's burned, you can remove the cover (if the amp is not under warranty) and look at the power supply components to see if they're burned. And... don't let a bad previous repair fool you. I always recommend cleaning all of the soot from an amp that made a mess when components failed. In many instances, a previous repair tech only replaced the minimum number of power supply FETs and didn't clean up the mess that the failing FETs made. If you're not careful when doing the initial check (to give a quote), you may think there is more damage than there actually is and give a quote that causes the owner to decline having it repaired.
  Quick Check Before Doing Anything to the Amplifier, Internally:
  Many times, an amplifier will be in good working order and a problem with the installation or speaker (pinched speaker wires, open/missing tweeter on 12dB/octave XO...) will cause the owner to think it's defective.
  To eliminate this as a possibility, you need to power up the amplifier to determine if it is functioning properly. You can do this by connecting it to a power supply (watching current draw very closely, initially).
  This Next Test is to Protect You Against Liability:

  Transformers in car amplifiers can short between windings and those short circuits can be intermittent (so, not immediately obvious). This can cause the 12v B+ supply to be driven to the RCA shields of some amplifiers. This fault can be intermittent and can cause car fires. It's rare for the problem to result in serious damage but there's no point in risking any problems with tests/precautions that take well under 1 minute to perform.
  If, when powered up, the amp is drawing the expected idle current for the type of amp you're testing (you'll learn what to expect as you get more experience), use a multimeter (black meter probe on the main ground terminal of the amp) to confirm that you read 1000 ohms or less to the non-bridging speaker terminals of the amp.
  If you read 1000 ohm or less, measure the DC voltage to the input RCA shields. There should be essentially no voltage (just a fraction of a volt, at most).
  This next paragraph has a link. Go back and read it. The device it describes is to protect you from liability. If you have nothing to lose (legally, financially...), ignore the advice.
  If there is no DCV on the RCA shields, connect a signal source (preferably with the shield ground protector seen at the top of this page) and, with your scope (set to 5v/div and 2ms/div) check for audio on the bridging speaker terminals.
  If you see clean audio on all channels, connect a properly protected speaker (description just a bit below) to the individual channels and check for proper operation.
  A Bit More Checking — Potentiometers and Switches:
  When checking for proper operation, operate all pots (potentiometers) and switches through their entire range to check for intermittent problems with the various controls. It's very common for a dirty pot or dirty switch contacts to cause one or more channels to drop out. If the amp has no output, the only thing that it may need is the cleaning of a switch or potentiometer.
  Cleaning switches can generally be done with only the bottom cover and possibly the end-plate removed (no further disassembly needed). If the owner of the amp complained that a channel was intermittent, very lightly touch/wiggle all of the controls. This will help identify intermittent operation. If the first thing you do is move the actuator through the various positions or rotate the potentiometers through their full range, it could clean the contacts well enough to make the pot/switch seem OK. Touching it lightly may save some time with troubleshooting when dealing with intermittent contacts.
  If you know that a potentiometer or switch is defective and new replacement isn't readily available. The Potentiometer Dissection page may be of interest. Cleaning of various types of switches can be found on the General Repair Notes - SoundStream page. See also, TT9, item #25.
  • Notes:
  • The above paragraph can save time. If the problem is simple and you un-necessarily separate the transistors from the heatsink, you MUST remove all of the old heatsink compound from the heatsink, insulators and the semiconductors and replace it with fresh heatsink compound. For larger amps, this can take an hour or more. This is a common mistake for those new to repair work.
  • Although this section is about testing before the amp is repaired (where it needs to be disassembled to be repaired), you should use the same procedure if you have repaired an amp and all seems to be OK but there is no audio. What may initially seem to be a significant problem may only be a switch in the wrong position or dirty contacts. The master/slave switch on amplifiers has cost many technicians lost time, especially when the master/slave switch is on the opposite end of the amp from the other switches.
• Verdict? Pass or Fail?
  If the amplifier works perfectly, you'll give it back to the customer. You will find amps in perfect working order fairly often. If you find problems, you can troubleshoot without knowing any more about the amp but it may help to know why/when it failed. It may reduce troubleshooting time (you won't be looking for internal reasons for the failure) and may be able to prevent the damage from happening again.
• Ask About the Amplifier's History:
  Sometimes, it helps to know about the amplifier's history. If you know what caused the failure (got wet, connected to B+/ground with wrong polarity...), or when it failed (when driving it hard, when speaker wires touched...), can help you more quickly troubleshoot the problem. If the amplifier was new out of the box and never worked properly (don't confuse this with new amps that were improperly connected and damaged), there could be a factory defect. I've seen amps with bridged solder connections (bridged with solder) and connections bridged with leads cut from the board. Both were manufacturing defects.
• DOA, Out of the Box:
  Sometimes, amps that are defective from the factory are difficult to repair. As you repair amps, you'll find that many component locations are vacant. This is commonly done (same board used for models with varying features...). When an amp is DOA, it's sometimes hard to immediately know precisely why. Unless you know the amp well, you won't know if the vacant component location is normal or if the missing component is the cause of the problem. You can sometimes see solder connections that have been disturbed for a missing component and that can help lead you in the right direction.
  This is one reason that you must know the individual components (especially ICs) well. You can sometimes blindly find a fault by finding a shorted/open diode or out_of_tolerance resistor. You won't be able to do that with a missing component (one of several) if that missing component is required for an IC (like the PS driver ICs) to function.
  Of course... If you can find a service manual or schematic diagram for the amp in question, they will typically tell you if a part was supposed to be left out. The part in the diagram could be absent, could be there with no value or with some note like 'no stuff' (no part will be installed into that location). The term 'populated' may also be used when referring to the installation of parts into a circuit board.
• If the Amplifier Needs Some Attention, Open the Amplifier:
  Again, if the amp is not under warranty. Check to see that the board is in relatively good condition (no areas where the fiberglass has been carbonized, no cracks from impact — as you'll often have if the amp was involved in an accident...). If there is an area where there is a blanketing of soot from blown power supply FETs, clean it up with solvent (more on this later) to make sure the board is still in good condition.
  If the amplifier got wet and there are signs of corrosion, you need to determine if it's worth repairing. If you see more than minor signs of corrosion, you need to pull the board and examine both sides before committing to a repair quote.
  Knowing if someone opened the amplifier before you is also important. For some reason, people who know nothing about the operation of an amplifier will turn all controls fully clockwise. Many think they're 'turning up the power'. These internal controls are typically 'bias' pots (potentiometers) and are there to set the idle current.
  The bias pots are analogous to the adjustments on a gasoline/diesel engine that set the engine's idle speed. When set properly, the bias pots allow the proper idle current to pass through the output transistors when the amp is not producing any audio. When someone sets the bias to the maximum point, it's much like someone setting the idle control on an engine so that the engine always runs at full RPMs.
  In an amplifier, the symptom for this is excessive current draw. If you cannot initially find a fault (shorted transistors, etc...) and the amp is drawing excessive current and the amp has bias pots, check them to see if they're set fully clockwise. If they are, set them to center or fully counter-clockwise to see if the idle current decreases. Bias adjustment will be covered on the Audio Troubleshooting page. There you will see examples where the full counter-clockwise setting won't be the minimum bias setting.
• Check the Terminal Blocks:
  I know that this may seem trivial but it's vitally important. After you've determined that the board is in good condition, you need to check the terminal blocks. If the terminal blocks are not in good condition (especially the B+ and ground terminals), the amp will not be usable† after you repair it. Many terminal blocks are not available so a stripped block can be a serious problem. For every screw in every terminal block, run it through its full length and make sure it can be tightened securely.
  For some blocks with short screws, you may need to insert something (piece of wire, screwdriver, hex key wrench...) into the block to allow the screw to be tightened without falling through. If there are missing screws, be sure that they're available before repairing the amp. Some screws are odd sizes and are essentially custom made. If any of the blocks are stripped, you must discuss options with the owner of the amp before you begin repairs. The Terminal Blocks page of the tutorial will provide more details.
  Again, this is not trivial. Unless you're a very mild-mannered person, you're going to be very angry if you spend hours getting an amp repaired, only to find out that one or more of the sockets in the terminal blocks are unusable. Check the terminal blocks before continuing.
  †If the terminal blocks are damaged beyond repair and replacements are not available, the amp can generally be salvaged by running wires out of the amp. It's not an ideal solution but it's better (for most owners) than sending it to a landfill.
  While you're checking...
  Along with checking terminal blocks, check RCA jacks and fuse holders.
  Make sure the shields are not loose (where they can fall out) and make sure that the internals inside the shield are all as they should be. For the back of the jack, make sure that none of the conductors are broken or pushed out of place. Many times, exact replacements are not readily available and you will have to find a way to repair what you have if you want to complete the repair. The Tiffany style RCA panel jacks are sometimes a viable option.
  For the fuse holders, push all of the fuses all of the way in. Pull one fuse to see what 'all of the way in' should look like. When pushing the fuses in, make sure that the internal terminals are not being pushed back out of the fuse holder housing. If the internal terminal is trying to move back away from the plastic body of the fuse holder (as you push the fuse in), either replace the fuse holder or hold the terminal from the back as you push the fuse in.
  Amp Owner's, in General:
  There is no 'general' type of amp owner. They vary widely. Some are happy to have an amp back making noise (reliably). Some will not pay unless the amp is brought back to 100% OEM working order. This means that they will not pay unless all mechanical aspects, as well as the electronics, are functioning perfectly. If you find something like an irreplaceable terminal block that cannot be repaired to be in 100% original condition (functionally), you need to discuss it with the owner before you find that he will not pay for the repair due to some small mechanical problem. Communication is key.
  This has been stated before but, it's best to communicate via email/text where a permanent record of what was said and agreed to is preserved.
• Check for the Most Common Failures:
  If, in the initial check, you found that the amp is in need of repair, you can make a quick check of the power supply transistors and the output transistors. Quickly checking for shorted transistors will give you a pretty good idea of where the problem lies. If you've ever seen a tech pull the cover off of an amp and use his meter to make a few quick checks, this is what he was doing.
  Power Supply Voltage, Ideal, Too High and Too Low:
  If you cannot find any shorted components, you will have to connect it to a 12v power supply as described above. The power supply voltage is stated as 12v and most any 12v supply will work but it's generally best to have a regulated power supply that's (ideally) variable but if it's not, you want a supply that will deliver a consistent 12-13.5v DC. Don't try to use a battery charger (too much electrical noise/ripple and can deliver 18+v under light load conditions).
  Some amplifiers have an upper voltage limit and will not come on above a certain voltage (most are OK up to 14.5v). Many amps also have a low-voltage protection circuit. Even if the supply has a no-load voltage of 11v or greater, the turn-on surge (due mainly to capacitors charging) can trigger the low-voltage protection and prevent the amp from powering up.
  You should also know that some amplifiers will refuse to power up if B+ and remote are applied at the same time. Amps that act in this way include some models of Coustic and Boston Acoustics (and likely others). You have to first make the ground and B+ connections, then apply remote voltage for the amp to power up.
  Note:
  Much of this is covered by flowcharts near the ends of the Power Supply Troubleshooting and Audio Troubleshooting pages. Don't forget that they're there. They can make troubleshooting much easier when you're new to repair work.
• Check the Voltage at Various Points:
  As a Primer...

  Many people take this step (checking supply voltages) too lightly. The various circuits cannot be expected to work properly if the power supplies feeding the circuits are not delivering the voltages they need. This is vitally important and literally takes just seconds in most amps. This applies to supply voltages in both the power supply AND audio sections of the amplifier. Sometimes, something will distract you from this.

  For instance, I was working on an MTX amp and found that one channel had a low level oscillation on it. I began troubleshooting the oscillation when the problem was actually a power supply fault. I wasted 10 minutes chasing down a problem that didn't exist. The problem was a defective transistor in the 15v regulator.

  Don't limit your checking to the various positive or negative supplies. One of the most important parts of the circuit is 'ground'.

  • There have been many instances where the ground was broken on...
  • The collector leg of the PNP driver transistors in the amplifier's switching power supply. In many of the older Orion amps where the collector connected to ground via a 10 ohm resistor, that resistor opened, breaking the connection to ground.
  • The ground terminal for the PS controller IC. For some reason this has happened more on the TLx94 IC but can happen on any of the ICs
  • The amplifier's primary B+ and ground terminals also need to be checked.

  When you power up the amp, you need to check various voltages. The first place to start is the power supply components. It's important that the various supply voltages are present for the amplifier to work properly (just as it's important that you have voltage at the wall outlet if a lamp plugged into the outlet is to work). In most amplifiers, the audio section requires more than the 12v that's available from the vehicle. Typically, you'll have plus and minus rail (±35-±65v DC) and ±15v for the op-amps and other audio ICs.

  The power supply transistors are driven by a dedicated PWM driver IC (in most amps). The PWM IC must have the proper supply voltages (from the vehicle's battery) to operate. The power supply transistors (FETs in most amps) drive the transformer windings. The transformer steps up the voltage. The rectifiers convert the AC voltage from the secondary side of the transformer to the rail voltage. The rail voltage generally feeds the ±15v regulators. If the power supply FETs are blown, in most amplifiers, there will be no voltage at any point in the audio circuit. JL, MTX and a few other manufacturers have amps that will produce voltage in the audio section if the power supply FETs are blown but they are exceptions.
• Confirm that Voltage is Present on Power Supply FETs:
  You'll check for voltage on the power supply transistors. For most amplifiers, the center terminal of the power supply FETs will have battery voltage (B+). The third terminal will be at ground (zero volts).† The first terminal should have ~zero volts without remote voltage. When remote voltage is applied, the first pin will have a series of pulses (if viewed with a scope — example covered later) and will read ~ 2-6 volts of DC if read with a DC voltmeter (DC voltmeter readings can be misleading).
  If you find B+ voltage (~12-13v) on the first and second terminals of the power supply FETs, and ground (zero) voltage on the third terminal, the FETs are defective.

  To say in a different way:

  If leg 1 = leg 2 = 12v and leg 3 is at ground, the FET has failed.
  This is important. The N-channel power supply FETs conduct when the gate (leg 1) voltage is approximately 3.5v greater than the source (leg 3) voltage. It the gate voltage is 12v above the source voltage and B+ is on the drain (leg 2), the FETs should be trying to pull the drain voltage to ground (leg 3). The amp should be drawing excessive current. If it isn't, the FET is open (defective). You will see this repeatedly in amplifiers and if you recognise this immediately, you will save yourself time troubleshooting.
  If there is no voltage on the first leg of the power supply FETs, ~12v on the second leg of the power supply FETs and the third leg of the power supply FETs is at ground (0v), the FETs are not being driven on and you'll have to determine why they are not being driven (assuming that the amp is powered up, including having remote voltage applied). All of this is covered in more detail on the Power Supply Troubleshooting page of the tutorial (don't click that link if this is the first time through the tutorial — you'll get to it in due time).
  †This is for the standard push-pull power supply with a grounded source terminal (3rd leg) for the PS FETs. You will see on the MTX power supply page that MTX and a few other manufacturers use (have used) a source-follower configuration. Don't get too concerned about the fine details at this point. Again, this is still the only first tech page of the tutorial.
• Check Rail and Regulated Power Supply Voltages:
  If the voltages are correct on the power supply transistors, you can check the voltage down the line. The rail voltage (this is the source that feeds the output power transistors) is going to be found on the rectifiers and the output transistors. You can check rail voltages at either point. You should have both positive and negative voltages in most amps (exceptions will be covered later). If one or both are missing, you have to determine why. Check for ±regulated voltage on all op-amps (again, there are a few exceptions where an op-amp will have only positive rail voltage — this will be covered later). The regulated voltage is typically between ±10 and ±18 volts. If you don't know which pins are the power pins, look up the datasheet for the op-amp in either the Semiconductor Datasheets. Navigate to repair_tutorial/semiconductor datasheets† in the tutorial with the Windows file manager (Windows key + E) or search Octopart for the part number of the IC of interest. If you use Octopart, buy from the manufacturer authorized distributors.
  †I know that there is a mystifying () resistance to using Safari but it works so much better when clicking links to files and folders. Safari is the only browser that will do this, effortlessly.
  Regulated Voltage:
  In virtually every instance where you see a reference to the regulated voltage, you will see it referred to as ±15v even though it may be higher or lower. As long as you have both positive and negative voltage† and the voltage is at least ±10v and the supply voltages are of equal magnitude (above and below ground), the regulated supply supply is very likely working properly.
  †The plus/minus regulated supply applies for most amps with only a few exceptions. Some class D amps have a ±15 v supply for most of the preamp section and then transition to a single-ended (only positive 12v) just at the beginning of the class D circuit. There are amps without switching power supplies, low power, much like that in a head unit, that have only a positive 9v supply.
  Rail Voltage:
  You will find (±35v to ±65v for most class B and class AB amplifiers that are used for mids and highs in a car audio system. This is just a ballpark number for rail voltage. Voltage varies with the rated power >> higher voltage = higher power for any given ohm load. In most amplifiers, you find both positive AND negative rail voltage but in many class D amplifiers, you will find only a positive rail voltage. In time (as you get through more of this tutorial), you will quickly recognize when you should have a split rail (±rails) and when you should only have a positive rail voltage.
  Another Short Trip into the Weeds:

  After reading that the rail voltage in class D amps can be ±150v (or more), you might be thinking that ±65v is weak but that's a large amplifier, especially if it's a two channel amp rated to go to 2 ohms per channel.

  If the rails can be maintained (regulated rail voltage, no rail voltage sagging under load), that's about 500w/channel onto 4 ohms. A 500w/ch amp in a class B or AB amplifier will produce copious amounts of heat and will typically be very large to be able to dissipate the heat it produces. For a real-world example... The a PPI PCX2400, that's rated for only 400w/channel into 4 ohms, has a rail voltage of about ±59v (measured). An amp with a rail voltage of ±65v would be able to produce more than 500w/ch into 4 ohms.

  A class B or AB amplifier with ±65 rails is an impressive amplifier.
• Check for Signal at Various Points in the Amplifier:
  If the amp powers up normally and doesn't draw excessive current, you need to drive a signal into the amp (not important what it is, you need to have a signal to follow through the signal path) and see if there is signal on any of the channels (check it at the 'bridging' speaker output terminals or at the output transistors). For amps that have speaker protection relays in the circuit between the output transistors and the speaker terminals, you need to check the signal at the output transistors. Sometimes, the relays won't engage due to a fault and that would prevent signal from reaching the speaker terminals. If signal is missing from all channels, you may have a problem with the regulated power supply voltage, a switch may not be set properly or the gains may be set too low. If those are not a problem, you may need to check the protection circuits to see if the muting circuit is engaged. If the amp is producing audio to the speaker terminals and there is no significant DC offset, you can connect speakers or a dummy load to the amp and further check for clean audio.
• Determine the Point Where the Signal Ends or Becomes Distorted:
  If there is signal on only one channel or if one channel is distorted, you need to find where the clean signal for the defective channel ends. This can require that you follow the signal from the RCA input to the amplifier section. If you cannot determine how the circuit is laid out, try driving signal into the working channel only. You can follow the signal through the good channel to see how the circuit is configured. Using a Sharpie marker, you can make a mark on the various components to show the path it takes. Then by driving the other channel, you can determine where the signal stops or where it becomes distorted. Many times, you'll find that a defective/dirty switch or potentiometer is the culprit. Sometimes, the problem is a broken solder connection. Other times, it will be a defective op-amp. If you find significant DC voltage (over ~1/2v) on the output of any op-amp in the preamp section of the amplifier, the op-amp may be defective. There will be much more on op-amp troubleshooting later.
  Rockford Amps and DC on the Op-Amps:
  There is a note about DC on the RCA shields on the older Rockford amps. This DC will be on all of the preamp op-amps. Grounding the shields will remove the DC if the DC is from the Rockford Circuit design and not an op-amp fault.
• Before Giving a Price Quote:
  After finding the defective components, you should give the rest of the mechanical components on the amp a quick check. More on all of these problems will be covered in more detail on other pages of the tutorial. Don't start the actual/final work until you get the amp working well enough to do these checks. Any of these could make the difference between getting the amp repaired to the owner's expectations and having problems with an amp that's working, electronically, but not up to the owner's expectations (possibly absolute perfection).
  Remember, you need to know precisely what the owner expects before starting the repair. I don't know what path you're following through the tutorial so (in case you haven't seen it), I'll refer you to the TT1 page, item #4. It covers the initial checklist fairly well.
  The advice given in the previous paragraph could mean the difference between success and failure in the repair business. Ignoring it may not cause your business to fail but it WILL make it much less profitable. If you complete an extensive repair and find that there is a problem with a terminal block or switch (either of which may be unavailable because it's a custom part and the manufacturer won't sell it to anyone) and the owner won't pay for an amp that is not 100% repaired, all of the work you put into it will be lost. If the leads on the parts that you installed were cut to fit the amp (that you won't get paid for repairing), they may not be of any use, even if you remove them. Don't get lazy. Carefully check everything before spending time and money on the repair.
  If the amp is completely inoperable and you cannot check the various components (particularly, the ones that may be unobtainable), remove the parts preventing the amp from functioning and test. If the power supply is inoperable, pull the defective parts and install just enough to get it working. This is a good use of parts that survived another repair but couldn't be used because you needed to have matching parts.
• Replacing Component Parts:
  After you find the defective components, you'll have to replace them. This will be much easier if you have good equipment (soldering iron, desoldering pump, high quality solder... — all of which is covered on the Equipment page). You also need to use good quality replacement parts. Exact replacements should be used. Do NOT use NTE or other generic replacements. Do NOT buy electronic parts from eBay/Amazon unless you know that the seller is reputable or you hear from an experienced technician that the parts are not counterfeit (MANY of the FETs on eBay/Amazon, especially those from Hong Kong and China are counterfeit or don't meet spec). Don't let feedback guide you on eBay/Amazon. Many of the people who buy electronic parts on eBay/Amazon do NOT know what they're doing and will give good feedback without knowing whether the parts are 100% legit and meet spec or not.
  Again!
  No NTE, no eBay or Amazon for semiconductors.
  If you use Octopart, buy only from the distributors that are authorized to sell the selected parts by the manufacturer of those parts. This will help ensure that you get genuine, first-rate replacement parts. The authorized distributors will have a green-framed star to the left of the listing.
• Bench Testing:
  When you get an amplifier repaired and reassembled, test it thoroughly. After it's gone through basic testing and reassembled, let it idle for at least 15 minutes. If you have other work to do in the shop, let it idle while you get those done. Letting it play at very low volume will allow you to know that it's on and nothing strange (noises, cutting out...) is happening. During this time, try moving the larger components, twisting the transformers and inductors, tapping on the board (with a non-conductive probe) to make sure that there are no intermittent problems. While it's playing, beat on the heatsink to subject it to vibration to make sure it doesn't have any broken connections. After you're convinced that the amp is OK, drive it for at least an hour at high power. Testing for an hour will help ensure that you didn't miss anything. You want to make ABSOLUTELY sure that it's repaired properly.
  • Notes:
  • Above, you may have skimmed over the 'twisting' of inductors and transformers but this is not trivial. A shorted transformer can cause you serious problems. This is why grounded shields and a visual indication (read ALL of item #11 on that page) of a problem are important.
  • It was suggested that you beat on an amplifier's heatsink when testing to confirm that there were no intermittent problems. Do this with the side of your clinched fist, not with a hammer (trivia? Legend has it that Rockford used to use a rubber mallet to test their amps for intermittent faults). Also make sure that there are no loose connections to the amp. When you're beating on it, it may move significantly. Any loose connection (scope/meter probes, remote, power, ground...) could allow a wire to break loose and short to something in the amp. This could cause significant damage and the troubleshooting could be significantly more difficult than standard failures (blown power transistors, etc.).
  • When testing, I'd recommend running the amp into a dummy load that's 2x the lowest rated impedance for the amp (2 ohms for a 1 ohm amp) and driving the amp (with music) to a level that has it clipping regularly (not constantly but on a consistent basis on music peaks). If you're using a signal source with a stepped attenuator, one position may be too low and the next too high. If this is the case, use the gain control on the amp to fine-tune the level.
    For a 'music'<Isource, I like Bass Boy - Rebel Bass. << Search YouTube for that exact text (in green) if you don't know what this is. It has good bass and a good overall balance of bass to lower level content... and no foul language (good if you're monitoring the audio and have customers coming into the shop).
  • Set Up A Second Bench:
    There will be times when you have an amp that has problem after problem but you finally get the amp working reliably... You hope. Don't return it to the owner without extensive testing. Some techs have only one 'bench' set up and that's where they work. In some instances, that will not be enough. For amps like the one described, you should let the amp run on a second bench that you set up for just such a situation. At the very least, you need to have the amp playing at a low level. For really troublesome amps, don't just let them play for an hour or two. If the owner isn't in a rush to get it back, play it whenever you're in the shops for days, even a week or more. If the second workbench location doesn't have enough of a power supply to run the amp hard, occaisionally bring it to your main bench and run it hard for 20-30 minutes. Then return it to the other bench location and let it run again.
  • For Amplifiers with Intermittent Problems:
    Most of us have moved away from testing with speakers (especially for hours-long tests) but they still, sometimes, serve a useful purpose. Some amplifiers have intermittent problems that seem to go away on their own or go away after you've done something to resolve it. The resolution of the problem could be coincidence. If you're not 100% confident that the intermittent problem has been resolved, play the amp into speakers that can cause the amp to be shaken by the bass. At first, do this at moderate volume and with a reduced rated fuse. This will help protect the amp if the problem returns. After a period of time that you deem sufficient, go to higher power. For my testing, the woofer was under the workbench so the amp got a pretty good pounding (possibly because the 3/4" plywood flexed fairly easily). When testing, go the extra mile to ensure that the owner gets the repair quality that he expects.
    Cheap 12v Power Supplies:
    If you don't have a second 12v power supply, there are multiple inexpensive options. If you have an old computer that you won't use again, the power supply in it may be usable. If not, computer and other switching power supplies are available on eBay. Search for 12v switching power supply. The supplies are about $1 per amp of output current. Buy one that's rated for 30 amps or more. While most of these are set at 12v, many can be modified. The server supplies that are rated for 100+ amps of current are sometimes available, already modified. If not available, outright, the modifications are often available online.
  • Idle Current:
    One of the questions I get repeatedly is for the idle current of amps and I don't generally have answers. Above and throughout the tutorial, it will be suggested that you take notes and organize that information. Read that entire section and follow all links. That will help when you see multiple amps of the same model. When I can't help and you don't have notes for the amp, you can take advantage of resources like the manufacturer's website, the owners manual or service manual for the idle current of an amplifier if you're concerned that it's drawing too much current at idle. The failure of manufacturers to provide this type of information is what makes it necessary for you to take notes and keep them organized (and backed up on a completely separate drive/system in case you get a virus or drive failure). I know... repeating myself but in regards to this, it's not enough. People refuse to take notes and photos. I don't know your opinion of this tutorial but if I hadn't taken notes and photos (due to a very poor memory), it would have been impossible to produce.
  One of the worst unforced errors that you can make is to return an amp that isn't properly repaired. If it fails after you repair it, it will be a strike against you (deserved or not). It's hard (almost impossible) to shake a bad reputation if you're just getting started (assuming that you want to continue doing this type of work). You don't want to have a reputation as a person who does shoddy work.
  Bill Padding (cheating customers) and Your Reputation:
  While on the subject of reputation... You absolutely do NOT<Iwant to pad a repair bill by misleading the owner. This is an absolutely disgusting practice and will ensure that you will have a bad reputation (and won't help the general reputation of other techs). One example of this is replacing capacitors. If the owner asks about the capacitors, you should check a good sample of the various capacitors and tell them whether the caps need replacing — or not. If you tell the owner that the caps are perfectly OK and they are willing to pay extra for parts and labor to have them replaced (without being lied to, to force/bully them into it), replace them. Please don't be dishonest. 'TV repair men' have a bad enough reputation for shoddy business practices. Don't be part of that group. If an owner sees that you go out of your way to deal honestly with them, word will spread.
  Remember the capacitor plague and think about all of the thousands (millions?) of perfectly good capacitors that were replaced with capacitors that will most definitely fail (where the originals would likely have still been perfectly fine). Who knows how many of those plague caps are still on the shelves?

• Notes/Review:
• Before you begin replacing parts, you should make a quick check of the switches and pots. Make sure the pots operate smoothly and don't spin endlessly. Most pots have a 270° rotation. If it rotates 360°+ and it's not a rotary encoder, the pot is defective. Rotary encoders click every few degrees and rotate with no stops. If the pot is scratchy (you can feel that it hesitates or is difficult to turn at one point in the rotation), it's not likely to work properly and will cause the audio to drop out at various points). Make sure that all switches move freely to all positions. When you get the amp working, recheck these BEFORE reassembling the amplifier.
• When dealing with multi-channel amplifiers (especially 3/4/5 channel amps), there may be multiple settings that will send signal to the individual channels. For example, a 5 channel amp may be able to drive the sub channel via a dedicated set of RCA inputs or from the front/rear signals depending on the settings of the switches on the amp. If you have a channel that's distorted (or otherwise defective), try using several settings. If the amp produces clean output with one setting but it's distorted with a different setting, the amplifier section of that channel of the amp is OK and the problem is in the preamp section. The channel would never play cleanly if the problem was in the amplifier section of that channel (unless it was an intermittent problem).
• Testing components with a multimeter was mentioned.
  When using the meter on ohms or or diode check, you should not have power applied to the amplifier. If voltage is present, it will skew the readings. Even residual voltage (stored in capacitors) will skew the readings. Many times you will have to wait for the capacitors to discharge before you can get reliable readings. In some amplifiers, 'you' will have to discharge the capacitors (through a dummy load or other resistor) to get them to fully discharge.
  When measuring voltage (to confirm power supply voltages and such), you will have power applied to the amplifier (including remote).
• When following signal through the amplifier (set for full-range use — no crossovers), the signal will look like the input signal (only varying in it's amplitude) until you get to the actual power amplifier section. When it enters the 'differential amplifier' section of the amplifier (to be covered later), the signal may look nothing like the input signal but still be perfectly fine. This is due to the way the differential amplifier and other parts of the actual power amplifier work. Tracing the signal beyond the differential amplifier can be tough. For beginners, it's often easier to locate defective components than it is to find the problem by signal tracing. Even for experienced tech, it's easier to look at the DC levels and the circuit topology than it is to try to follow the signal through the amplifier.

Don't get discouraged if you're lost at this point. This page is nothing more than an introduction. I will begin filling in the blanks and going into much more detail. Continue reading the pages in order and the overall operation of an amplifier will become much more clear. If you want the following page to work as smoothly as [insert something that's really smooth here], switch to the Safari browser before going to the next linked page. It makes everything work so much better. You can use other browsers and eventually get the destinations to work but with Safari, click and it's done. In the directory, there is a link named Images and Notes for Other Amplifiers.† Below that are links to pages with information on individual amplifiers. In the miscellaneousstuff folder there are files/folders for more than 100 different amplifiers (thousands of photos). Some pages have thumbnails and links to larger, higher quality images. For others, the high resolution images are in the folders. For many amps, you will find notes for common problems. †For reference and to make it easy to find, this page is 2 chapters above the Website Section directory. The link (has a blue underline) to the '- Directory - Website Section' is provided on the home page of the tutorial. This section of the directory is easily identifiable as you scroll down in the main directory because chapter icons end at the website section. The page you want has a white icon with a few amp manufacturer names. The page includes a significant amount of information about using Windows (for those who only know how to use Android or iOS). For those who know Windows well, you can click the 'MiscellaneousStuff Quick-Links' link at the top of the page to jump beyond the Windows instructions. The amplifiers range from the very old (mid 1980s) to some relatively new models. If you read through all of the pages and look at all of the images, you will become more familiar with amplifier layout and common problems. Click on any files in the Windows file manager folder. swf, gif, png and jpg files are graphics files. txt files are text files (will likely open in Windows Notepad) htm and html are website type files (which will open in your default browser unless you select a different browser). Before working on any amplifier, you REALLY need to browse the folder(s) for the manufacturer of the amp that you're repairing. You may not find the exact amp you're working on but similar amps may have similar problems and the notes may help you from making mistakes. When you open a sub-folder in the miscellaneousstuff folder there may be many files and you'll have to search for the txt or htm files. If you sort the files by date modified (most recently modified at the top), the txt and/or htm files are likely to be at or near the top because they're the files that repeatedly get modified/edited. If you don't have a good graphics viewer, use Irfanview. When it's being installed, it will ask you about file associations. Select only JPG, PNG, TIF and GIF. De-select all others until you decide that you like the viewer.

• Irfanview allows you to:
• To step through images by clicking the space, backspace or left/right arrow keys on your keyboard or rolling the mouse scroll wheel.
• To zoom in, hold the ctrl key down and roll the mouse scroll wheel.
• To navigate through the photo easily while zoomed-in (for very large images) use the right mouse button and drag the image.

Another good viewer is the FastStone image browser. It's also free. Both of these viewers allow you to step from one image to the next with the mouse scroll wheel. If you are going to view more than a tiny fraction of the images, this will be a very important feature. The images in the individual amplifier folders are typically very large. It is unlikely that your monitor will be able to display them at full resolution AND have them fit to the screen. There are two options. You can allow the browser to resize them (and allow the entire image to fit on the screen). Or, you can allow the image to appear it's actual size and use the scroll bars to see all parts of the image. The first option will result in relatively poor resolution. The second option will give much better resolution. Back To The Top

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