All
modern versions of Windows are supposed to ship with the Gulim font but it seems that some computers are missing the file. The font is the best I've found for this tutorial it's clean and extremely easy on the eyes. If the text in this paragraph doesn't look like the
20px example below, I'd recommend installing Gulim. Click on the image below to go to the instructions and file link.
This is an image, not a block of text. 
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.
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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.
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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.
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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.
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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.
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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).
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Page Up/Page Down Key:
These step approximately one full page height per click and will repeat if held down.
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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.
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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.
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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.
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.
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.
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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.
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:
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.
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.
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.
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.
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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.
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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+ is the positive battery terminal connection on the amp or the positive 12v source (depending on the context).
TNFG means Take Nothing For Granted. Confirm everything that could make a difference for the circuit you're troubleshooting. Make no assumptions.
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.
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.
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.
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.
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.
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:
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Navigate to that folder and double-click the file to open it in the default PDF viewer
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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.
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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.
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Recommendation: PDF Xchange Viewer. It's fast, free and works very well.
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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.
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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).
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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.
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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.
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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).
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.
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.
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.
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.
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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.
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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.
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A link with this color underline is an internal link. It will open a new tab. To clear it, close the tab.
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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.
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.
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.
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.
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
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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.
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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.
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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.
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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.
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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).
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.
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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.
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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
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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.
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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.
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.
Bear in mind that misunderstandings can wreck business relations and ruin your reputation if the owner of the amp feels he has reason to slander your good name... And many people become vicious if they feel like they're a victim (justified or not). Remember that, nowadays, the goal of too many people is reaching the status of victim. Victimhood gives them a way to get sympathy and being on the receiving end of sympathy floods their brain with feel-good chemicals (dopamine?) which gives them (as an addict to those chemicals) reason to carry out a vendetta against you.
And while in the neighborhood of dissatisfied customers... If you repair an amplifier and someone refuses to pay you because there is some sort of conflict on the final repair,† do NOT pull parts and send it back with missing components if it was complete when you received it. This will give the owner a reason to ruin your reputation on social media or possibly through the BBB. Bagging and retaining all FETs until the repair is complete (repair paid, amp installed and working) is a good practice.
†One of the problems with repairing amplifiers is that some parts are no longer available. This is especially true for custom manufactured components (potentiometers [there are so many variables], terminal blocks...). There will be times when the amp has to be made functional but it may not look OEM. This is a problem for some customers.
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.
This tutorial is intended to give you an expansive knowledge base for most all types of amplifiers, not only one type of amplifier. Brazilian amplifiers and their Chinese knockoffs are popular (mainly because they're cheap) and you may be looking for information on the specific Brazilian amp you have. There are just a few specific Brazilian amplifiers here but they really aren't that special. Except for their microcontrollers,
† they use off
_the
_shelf semiconductors. In that respect, they're like most other manufacturers. They sometimes design their circuits a bit differently but, if you put forth the required effort to understand the components covered in this tutorial, you will rarely have trouble repairing one...
with the exception of finding the part numbers of defaced parts.
†It's bit early to go into details but the term microcontroller (
AKA MCU,
µ-com or microprocessor) refers to an IC that can be anything, with reference to control circuits. The pins on it can act as inputs or outputs and the ICs have to be sourced from the manufacturer or one of their distributors. They cannot be purchased from normal electronics parts distributors. Think of them this way... They are essentially the same as a big pile of lumber and building supplies. What are they going to be? They could be virtually anything. Without documentation from the manufacturer, you don't have a clue what the various pins are, except for the power supply pins. When you get a Brazilian type amplifier in for repair and the amp doesn't function normally, there isn't much you can do if the MCU is the problem. Add to that, if you damage the MCU accidentally and cannot get a replacement, you just turned the amp into a paperweight.
Initially, avoid any of the Brazilian amps with defaced parts.
† Only about half of the Brazilian type amps have defaced components. When defaced, the original markings will be sanded/ground off and (generally) a single alpha-numeric mark will be stamped into the face of the component. For amplifiers with re-marked components, tell the owner what the manufacturer did to the parts and that he will have to return it to them for repair. This is not a reflection on your ability to do the work.
†Initially, avoid any of the Brazilian amps with defaced parts.
<< Repeated intentionally.
THIS link is a meeting place for most all of the Brazilian-specific amp information. Read that entire page (not just from that link's landing point). Follow the links on that page and perform the searches as suggested and you will find quite a bit of relevant information for Brazilian type amplifiers.
These two ICs, when the output transistors are defaced, are some of the most problematic because if you can't determine what the original transistors were. This is because you will have to re-calculate the protection circuit components and/or perform extensive testing (possibly destroying various components) to ensure that you have properly repaired the amplifier.
Virtually no one will do this as they should
† and why I recommend that you avoid any amplifier with defaced transistors, especially if the driver ICs use the on-board over-current protection.
†When I asked why different techs weren't doing this, I received responses, some of which bordered on being abusive. Some people become irrationally defensive when you question their competence.
Most amplifiers use current shunt resistors and an external comparator (all to be covered in detail as you work through the tutorial) to detect over-current. This allows the use of virtually any replacement FETs of sufficient voltage rating... at least for initial testing.
Most of the amplifiers that use the 2092/20957 ICs utilize the internal/on-board over-current protection. If you have a bank of output transistors that has no FETs in it, the amp is likely to go directly into protect mode. This prevents you from checking drive signals, as you could with other types of class D amplifiers. If you try to use replacement FETs that are not identical to the original FETs, the amp could misbehave in a couple of different ways. It may go into protect prematurely (possibly even on startup) or it could fail to go into protect when it should (shorted speaker or wiring...). Ways to make these ICs behave well enough to allow proper testing will be covered in detail, later in the tutorial.
If you're working with an amp with defaced FETs and cannot get definitive answers on their part numbers,
THIS page give some options. If this amp is likely a one-off repair and you're unlikely to see any more like it, it's not likely to be worth the time/effort to repair it
properly. Let the owner send it back to the manufacturer or their authorized repair center.
To cater to those
interested only in Brazilian amplifiers, I've tried to include the word Brazil in the text related to components and circuits commonly used in Brazilian amplifiers. Perform a
ctrl-f search for
Brazil on each page of the tutorial to see what relevant information there is for those amps on that page. This isn't the right way to learn to repair amplifiers but the request is so common that I've given up fighting it.
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.
Click
HERE to open this graphic in a new tab. Right-click to zoom. Left-click to drag.
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.
There is a good chance that you will ask me to help you with repairs.
This is expected. One problem that needs to be avoided is sending me poor/erroneous/incomplete information. One of the worst is when I ask for voltages and people are too lazy to give exact meter reading. Now, I don't want the exact meter reading if you're using a
Keithley 2002 meter<Iwith 8 digits to the right of the decimal (2v range) but I do want/need the 3 digits to the right of the decimal when asking for meter readings... even if they are zeros If you're using a standard multimeter, give me precisely what's on the display for whatever reading I'm asking for (voltage, resistance, diode-check readings on components...).
I know it's generally an ancient concept but
common sense is important. Use what you have and develop that ability. Think logically. On far too many forums, I've seen people throw out suggestions that made very little sense and were only very rarely useful (and even then, only by luck). When you start to make a change, of any type, carefully think about what you're trying to achieve and whether the proposed change will do what you want.
Ordinary sensible understanding; one's basic intelligence which allows for plain understanding and without which good decisions or judgments cannot be made.
The American Heritage® Dictionary of the English Language, 5th Edition
Don't do anything blindly.
† If that's how you're going to try to do this work, you have very little chance of ever being a competent technician.
† If you don't perform tasks/troubleshooting in a logical manner and ever encounter a real tech, you'll be considered to be a hack, or worse.
†Initially, you will use what you know to think through various problems, replacing only those parts that need to be replaced. Occaisionally you may encounter problems that could use a bit of guesswork but those are rare. If you are struggling with troubleshooting a problem, email me and I'll try to help. Troubleshooting via email isn't perfect but it's generally successful.
†You'll see the word 'competent' used repeatedly. There are people who can get an amp back to functioning but far fewer who completely understand the circuits and strive to deliver an amplifier that's at least as good as it was originally. Slight improvements can often be made in the protection circuits to make the amp more reliable. The information provided in the tutorial is what the average working technician would know after several years in the business. The knowledge would likely cover different amplifiers but the level of knowledge would be equal.
If you're asked to provide the
voltage on various points in a circuit, unless otherwise directed, you must have a 12 volt
† supply voltage applied to the B+ and remote terminals of the amp and the amp ground connected to the ground terminal of the 12v power supply. Rarely, you may be asked to leave the remote terminal with no voltage applied (so the amp wouldn't power up normally) but, again, that would be rare.
† Powering only remote (no 12v supply voltage connected to the B+ terminal of the amplifier) is common when checking power supply drive signals in older Rockford amplifiers.
<< Ground isn't mentioned but you will never likely be asked to power up (in any way, for any reason) without ground connected. There is an advanced form of troubleshooting that will require not having the amp grounded but that is not performing any test on the amplifier, as an amplifier. It's used to find defective components.
†'12 volts' (12v, B+, anything similar) is going to be a generic term used for the power supply for amplifiers throughout the tutorial. This is adopted from the 12v automotive charging system which isn't exactly 12v but that's an easy way to refer to it. Car amplifiers are typically designed to operate from about 10.5 volts DC to about 16 volts DC because the actual charging system voltage in a vehicle can vary quite a bit. Anyway... 12v in this context means a DC power source that is of suitable voltage (12v-13.5v, is optimal) and current capacity (will vary greatly depending on the task at hand) to power-up a car amplifier.
†This is for amplifiers that have only the remote turn-on input to control the amplifier being on/off and without that remote voltage, the amplifier's power supply (and therefore the amplifier) would be shut down. There may be amplifiers that use signal-sensing on the RCA inputs (may be used if you're using a cell-phone for the signal source, which has no remote turn-on voltage to send to an amplifier) or DC detection (often used to sense when an OEM head unit with a bridged internal amplifier is being used as the signal source). The second two examples are a different can or worms, so to speak
Above, '
B+' was noted as a possible 12 volt designation (as
B+ and ground). When you see B+, look at the context. For the input to an amplifier, it's
12 volts. If you see it as the designation for the positive supply terminal of a 'chip' (
Integrated
Circuit,
IC...),
† it could have a different meaning. For example, you will see circuits with positive and negative supply voltages of
B+ and
B-. In that context, the
B+ would be a
+15v supply and the
B- would be
-15v and having a negative component, you would know that it comes from the
output of the amplifier's switching power supply. I know that much of this language is foreign to those new to amplifier repair work but just read along and all will become clear.
Click
HERE to open this graphic in a new tab. Right-click to zoom. Left-click to drag.
†The terms/abbreviations
chip,
IC,
I.C.,
Integrated Circuit may be used interchangeably through the tutorial. The term 'chip' is not really acceptable when referring to ICs so I'm trying to replace it where appropriate. Where it is more acceptable is when referring to small SMD (Surface Mount Devices) i.e. chip capacitor, chip resistor...
Sorry for all of the clarifications but some people are very new to electronics and this needs to be done. The
±15v specified in the previous text is another generic value. This is intended to be the supply voltage for the various preamp ICs like
op-amps. The actual voltage can vary. Rockford uses supplies as low as
±9v (specified as
±9 but actually a bit higher). MTX commonly uses
±18v.
±15v is nothing more than another generic value like
12v was used, above.
When I was just starting out, the concept of negative voltage was very confusing. It shouldn't have been. It's all about a reference point. If you're in a 3-story building and on the second floor, you can easily understand that you have one floor above and one floor below. Voltage is all about reference points and for a multimeter, the point where the black probe is placed is the reference.
If you have two
D-cell batteries in a flashlight, stacked end to end (connected in series), the flashlight will operate off of 3v (each battery is 1.5v). If you place the black probe on the negative of the 'bottom' battery and touch the top terminal of the top battery with the red probe, you will read 3v. If you touch the black probe to the center of the two batteries and the red to the negative terminal of the bottom battery, the meter will read
negative 1.5v...
Enough Blah, blah, blah...

Click
HERE to open this graphic in a new tab. Right-click to zoom. Left-click to drag.
If the amp has on-board fuses, all fuse holders should be filled with the correct fuses (as designated by the manufacturer). All fuses should require a bit of force to insert and remove them. A loose holder could cause an intermittent connection or could cause the holder to overheat and melt, making it unusable. This can present a problem for you if you repair the amplifier only to find out that the holder is defective and not available as a replacement part. This may mean that you won't get paid for the repair if the owner wants the amp back to original condition.
You should read 0 ohms
(or whatever your meter reads when it's set to ohms and the multimeter probe tips are held tightly together) across each fuse when they are out of the amp. There are many amplifiers that have multiple fuses in parallel. For those, having a single good fuse when all others are blown would make all look good (read 0 ohms). If any fuses (out of the amp) read as open (no change in the meter display when the probes are touched across the fuse terminals), they need to be replaced. More on fuses can be found
HERE. Read down, at least, to ''.
Each time you use your multimeter (to check anything, for voltage, this is even more important), you should set the meter to ohms and hold the metallic probe tips tightly together. The meter should read less than 1 ohm. The resistance will typically be approximately 0.1
-0.2 ohms. That low resistance is the resistance of the meter's wire leads. What's important is that it reads very low ohms. This tells you that the meter leads are intact. If you have defective leads (or a defective meter) and go straight to testing for voltage and the circuit you're dealing with is high voltage (mains voltage, 110+ volts), not knowing for certain that the meter is reliable could be lethal. For most instances in car amp repair, a bad lead simply means a lot of wasted time.
If you're giving me part numbers, use upper case letters:
If you're sending me a voltage/resistance
/? meter reading and the display reads 0.345:
The negative symbol (
—) is very important. If the meter reads negative voltage, you need to include that. It will be assumed that all voltages are positive unless you make it very clear that they are negative. This simple omission can waste a huge amount of time. If you don't know what it looks like to have a negative reading, check the voltage across your 12v power supply with the meter probes properly oriented. Then reverse them and the meter will display a negative voltage (assuming that you're using a digital multimeter).
When you ask for help, you need to give the exact (EXACT) model number on the amplifier... NOT the model you
think you remember. This prevents wasting time from the assumption that the amp is one model but it's actually an earlier or later model with virtually the same exact model number.
Good quality photos of the main and any driver boards is also helpful.
Rockford has had a habit of stuffing the same board into more than one model amplifier. If your amp is a
Rockford, send the PC# as well as the model number. Finding a diagram for a particular board number is more likely to be successful than looking for a diagram using a model number. Sample PC numbers for older amps, PC-****-*. For newer amps 1325-*****-**. The 2-digit suffix is the revision number and not generally critically important.
When measuring voltage, if you're measuring the voltage on the
primary side of the power supply (
the '12v' side), using the primary ground (the connection to the chassis ground of the vehicle) as the reference is perfectly fine. For this, you will typically place the black meter probe on the amplifier's main ground terminal.
When measuring the voltage on the
secondary side (the
audio side of the amplifier's switching power supply transformer) you need to confirm that the primary and secondary are connected, to some degree. The most common connection is a
1kΩ (1000 ohms) resistor
between the primary ground (main ground terminal) and the
secondary ground (transformer secondary center-tap
† or the non-bridging speaker terminals).
† If you measure 1000 ohms or less between the primary and secondary grounds, you can use the primary ground as the reference (placement for black meter probe) for your multimeter. If you read more than 1000 ohms between the primary and secondary grounds, use a secondary ground as the reference.
†Not 100% reliable for more complex amplifiers. For basic amplifiers (virtually all class B or class AB amplifiers) there is only one secondary center-tap choice. It's the same as the secondary ground. For more complex amplifiers, it's common to have
secondary windings in series. Amplifiers with this transformer configuration will have significant voltage on their center-tap windings. Instead of being a secondary ground, they are actually the output windings from the previous series-connected transformer. For multimeters, it makes no difference if you place your meter's ground probe on the '
hot' secondary center tap. For a
mains-powered scope, it's a huge problem. This will be explained in excruciating detail on the Switching Power Supply Troubleshooting page. If this is the first time through the tutorial, continue below. If you've already read through this entire page, click
HERE. Continuing to go on to item #39 of that page
will be overwhelming for most rookie techs.
†The
non-bridging speaker terminals are highlighted by the red arrows in the image below. For this diagram, they use the
BTL designation for bridging. The bridging terminals are the left positive and the right negative. As you can see by the heavy/thick black line connecting the other two terminals (the two terminals that are NOT used for bridging and the ones you would use as the secondary reference), they have a direct connection
† to each other and to ground (heavy black lines are typically ground). These lead back to the secondary ground.
THIS is a partial diagram showing the heavy black ground lines back at the power transformer. These images were taken from the
Sony XM-1004 service manual.
†Initially, you can generally find the non-bridging terminals by finding 0 ohm continuity between the terminals but remember that the non-bridging terminals will be
one of the
positive speaker
terminals and
one of the
negative speaker
terminals of the amplifier. Confirm that those terminals also read 0 ohms to the secondary winding of the power transformer.
When troubleshooting, especially when you have very little experience, do as much work as possible with the heatsink-mounted components
tightly clamped to the heatsink. This will greatly reduce the risk of component failure from overheating (which can sometimes happen within just a few seconds). The components referred to here are indicated below. Of course, those in the photo are not clamped to the heatsink and would be at risk of failing unless you were paying very close attention to their temperature (it's easy to get distracted and to forget to do this).
Click
HERE to open this graphic in a new tab. Right-click to zoom. Left-click to drag.
When you're measuring the voltage on a circuit, you may find that, if you go back to confirm the values you found the first time through, those numbers aren't precisely the same. That's to be expected and you will nearly always double-check voltages when they're being used for troubleshooting. Various components are temperature sensitive. When an amp is run for any length of time, the components change in temperature. You shouldn't rush when doing this but you should get the readings in a timely manner and (when possible) after the amp has had power applied for about a minute or so... and run back through the pins a second time to make sure you have the voltages correct.
Many times, is not the precise voltage but the voltage in relation to the voltage on another point in the circuit. If you're told to place the black probe on a given point/component terminal, it's likely important that you do as instructed. If it's not possible, ask for suggestions.
An example of this
(^^^) is when told to measure the voltage on one of the power supply driver ICs and you're told to place the black probe on pin 7 but you figure that pin 7 is connected to ground so you'll just place the black probe there... well, not all grounds will be at the same voltage. If the voltage on pin 7 is a few thousandths of a volt from the ground pin and the voltages are critical, the voltage on pin 7 has to be subtracted from ALL of the voltages you give which is a huge pain in the... Not everything is as easy as clicking a 'like' button. Get used to it.
There is a page that's here to help you learn about reference points when measuring voltage. If you're brand-new to multimeters and repair work, it may be more than you need/want to know at this point. If you want to give it a quick look, click
HERE.
Don't use the '
continuity' mode on your meter.
Be aware that most techs don't want to do tech support. You may find a few who will, on a limited basis, but be mindful that they are trying to run a business. Unless you're paying them for their time, they're likely just being polite when they answer the phone or an email regarding tech support.
If they do try to help, offer to pay them for their time.
That doesn't apply to me. I'm retired and enjoy providing tech support to those who do what they can to
make the process flow well — the entire reason for this partitioned block.
If you're asked for a photo of the board (or anything else in the amp), don't send a blurry, poorly lit image (too dark, huge
[make that any] flash/light flare in the photo...). Take pride in what you do and do your best, realizing that your best may be at the sharp end of a steep learning curve. Continue taking photos (that cost nothing) until you get a good quality image with the components of interest in good focus/lighting. If the extra 10 minutes it takes to get a good photo isn't worth the time, the
amp evidently isn't worth repairing. After you learn how to take a good quality photo, it only takes seconds to get acceptable results.
One of the first tasks you perform do when repairing an amp is to remove all defective components. While there will be sections that give you a guide on how to troubleshoot amp faults, none of those will do any good if you don't know the components, how they're supposed to work and how to test them. This page will help greatly on learning those components and what to check for. Don't just skim over the information.
The statement above is fairly generic but below are some specific items that you have to know to make electronics repair work easier (possible
?). The knowledge you need to do this work isn't insignificant and acquiring what you need to know will take some real effort. Don't expect everything to be as simple as tapping a thumbs-up icon on a social media site (unless you have a 200+ I.Q.).
You can expect wasting many hours of your life if you
attempt to do this work without learning the basics. The items in the following list likely won't mean anything to you at this point (they will seem like random words) but you will understand them (very well) as you diligently work through the tutorial. If it takes a of doing nothing else but getting to fully understand the function of the next individual items as you come to them, take that
time.<IIt will save FAR more than that time in the future. Seriously,
expect to flounder in vain if you fail to learn/do the following.
-
The functioning of the switching power supply† driver ICs (IC = Integrated Circuit = 'chip'). The most important is the TL494/TL594/KA7500 (all VERY similar). People who have been working at this for 10 years, or more, still haven't taken the time to understand this IC and waste more time and money replacing perfectly good ICs than you'd believe.
It's as bad as replacing perfectly good capacitors, for no reason. This power supply driver IC has many different features but its response to the inputs on its pins is very predictable if you just take the time to learn how it works.
†Although you won't see it much in this tutorial, if you reference other technical websites or datasheets, you will see a switching power supply referred to as a DC-DC converter (or shortened to converter i.e. boost and flyback). The term converter is used because it takes DC voltage (12v in a vehicle) and converts it, ultimately, into one or more other DC voltages.
-
The function of op-amps (operational amplifiers). These are used in virtually every amplifier. They can be confusing if you don't take the time to understand them. The basics are easy and the more complex characteristics like knowing the precise output with varying configurations and resistor combinations can be understood with a bit of study. The op-amp page of this tutorial has interactive demos to help you understand the op-amp in most configurations.
-
This is one that I've just about given up on but it's such a wonderful thing that I keep trying. Using your mains-powered scope in differential mode... It's using two probes/channels (much like you do with your multimeter) of the scope to view a signal with more resolution than you can see, when using only one channel of your scope. It shows you the difference between two points in the circuit. This is somewhat easier for older analog scopes but if you know how to use your digital scope, it is easy to do.
-
The use of DC coupling on the oscilloscope is another pointless battle that I will continue to fight. If you're trying to determine if drive signals are acceptable with your scope in AC coupling mode, you may as well be using a bleeping Etch-A-Sketch.
-
Take notes and photos and keep them well organized. More on that, later on this page (and others).
-
-
The last of these (more of a tool than knowledge) is using a signal source with a properly grounded audio shield. You can still use your phone but you will need to make a SIMPLE adapter (that you should use, regardless of your signal source).
Although it may seem insignificant to have an un-grounded shield, it will be VERY obvious if having an un-grounded shield lets you send an amp out that applies high-current 12v to the head unit through the RCA shields. This can (and does) happen if a transformer shorts from the primary windings to the secondary windings. If the head unit has its RCA shields connected directly to the head unit's chassis ground, the RCA shields/cables can burn their entire length, from the amp to the dashboard. This can lead to significant damage, including the complete loss of the vehicle due to fire. The owner could hold you liable for that loss.
Spend the bleeping $10 and the bleeping 10 minutes to make this bleeping adapter. My 'swear jar' is going to reach a level that will allow a full retirement.
If the shields in their head unit were damaged, don't jump them with a wire. If the original circuit was broken/opened by burning a trace, repair it as shown on the Temporary Shield Repair page. If the original circuit had a fuse or poly-switch, repair it properly by replacing with the same type of device.
I try not to be too repetitive in this tutorial but you'll see me repeatedly rant about the items above... not because I want to annoy you but because I want you to succeed. You'll also see this again... If you're honestly interested in this type of work, you need to read this material like you want to know it, not like it's punishment for something that you didn't do. Let's hope you read it more carefully/thoroughly than the yellow section at the top of this page (that, according to records, has never been read in its entirety << a battle that I've long since given up on).
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.
Click
HERE to open this graphic in a new tab. Right-click to zoom. Left-click to drag.
...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.
This paragraph should not be necessary if you're thinking logically when troubleshooting an amp but it has happened so many times that it has to be included. When troubleshooting a problem and ESPECIALLY when asking for help troubleshooting a problem, you need to reduce the number of variables as much as possible.
One of the most annoying problems for me is when someone uses the amp's gain control to adjust the output of an amp instead of using the signal source's or some other inline volume control.
If you have a problem and email telling me that the amp shuts down or has some similar problem when you get the gain to x-position, expect a long delay for a reply...
if you get one at all. Use a proper signal source (preferably a proper head unit) that has its ground connected to the same ground as the amplifier being tested and
adjust the signal level with the volume control on the signal source.
When you adjust the level with the gain, you are introducing a second variable. The problem could be with the gain control or could be a problem that corresponds to a particular output level of the amp. If you think it's the gain control, set volume on the head unit to different levels. If the problem occurs at the same position on the gain control, the problem is likely due to a dirty or defective gain control. If the problem corresponds to the output level, that points to a different type of problem.
THIS link is for a section of the Potentiometers page of the tutorial and shows how to use a potentiometer as a level controller. I've been using
this type of volume control in the
Bench Switcher that I built back in 2005. It's always at hand and you can adjust the volume much more quickly than you can with any digital volume control. The example shows a Radio Shack part (which is still available, in limited quantities, on eBay and elsewhere in 2025) but virtually any potentiometer of 10k-100k will work perfectly. A logarithmic taper is ideal but not imperative. It's not even a requirement that the pot be a dual element component. There's nothing that requires a stereo signal for testing amplifiers.
The next image may seem odd for an amp repair tutorial but it may be one of the most important tools you have. This tutorial is about much more than just the repair aspect. There will be many tips that I wish I'd have heard earlier in my time doing repairs. Most are more valuable (for someone who will do this for more than a couple of weeks/months) than you can imagine.
When working on amplifiers, there will be times when components fail and that failure causes one or more parts to burn to a point where all markings are destroyed. This can be a problem when the manufacturer can't or won't tell you the value of the component or when the service manual/schematic diagram isn't available.
Most people won't use a camera and will refuse to use anything other than their beloved phones. Some phones can take photos as good as a camera but, even an old inexpensive camera like the one above, can get photo after photo effortlessly. This is a 20 year old
<I2MP camera and it takes wonderful macro photos. Not many of these are left but newer Nikon CoolPix cameras can do an even better job... again, effortlessly. Ask around, you will likely find people who will give you (or sell cheaply) an old camera they have laying around. Get yourself a good set of rechargeable AA batteries (likely what the old camera will use) and a charger. I used Eneloop batteries and the Eneloop Pro were the best AA rechargeables I'd ever used. Check
Battery Junction for reviews on batteries.
THIS link is to the photography section of the basic repair page online. It's likely that you've already seen it but you may want to read it again.
THIS is a link to my macro-photography page and goes deeper into taking photos of small objects.
Don't discard the photos that you take. Start a folder with sub folders that have the amp make, then the individual models. The
Rockford T1500 is an extreme but shows that a lot of data (200+ total files in 15 folders) is collected for some models.
When you take photos, be sure to take photos of the
faces/part numbers of the
original heatsink mounted components. Also take photos of the electrolytic capacitors in the amp... from the side showing their voltage rating, their value and whether they're 85C or 105C caps. This is something I failed to do, far too often. Many times amps are second-hand repairs and the parts are missing or could possibly be the wrong parts. If the manufacturer won't help, your photos of an identical make/model amp's components may be your only reliable source for the part numbers.
After taking the photos, look through them on your computer (or anything with a good monitor). Look at the various resistors (and other small components) to confirm that the photos are of sufficient quality to allow you to read the markings clearly. Don't just look at the center of the photo (where it's likely to be in focus). Make sure that the camera didn't focus on the
top of a tall capacitor
or transformer, leaving the resistors and such out of focus.
THIS
is a better photo of the area with the resistors in focus. Check the quality of the entire image. Also know that the parts that you feel are unimportant are, many times, the ones you need to ID so get photos of everything. There will be small, low-profile components that will obscured by larger components. Take photos from enough angles, move wires out of the way... to capture everything. The original photos of the reduced images above can be found in the JL 500/1 rev10 folder:
miscellaneousstuff/jlaudio/jlaudio500/jl 500 rev10/
Save the files at a reasonable resolution. You don't want files that will unnecessarily take up drive space. Adjust and remember the resolution you use for the best cost/benefit ratio (regarding storage space). Not only do you take up space with excessive file sizes, it takes longer to process them (building thumbnail databases, scrolling through images quickly...).
Start with this as a suggestion and adjust to suit your needs. Take the photos so that you can easily read the component values (markings on all SMD components and all resistors) at about 3/4 of the full size. It's easy to pull back to 75% in Irfanview and likely in other graphics software.
The photos of amps should be taken before you begin repairs. Sometimes, a part goes up in flames when you apply power. That can also happen after you replace a part that restores current flow to parts of the circuit that previously had none. Taking photos of the finished product is also good, especially if you replaced parts that were parts burned beyond recognition or
obscured by soot.
Although the previous paragraph focused on internal electronic components, there may be a few other items you may want to photograph. I had one 'collector' complain that I installed the bottom cover backwards (model/information/serial number label was on the wrong end of the amp). I did but it was insignificant... to me.. but not to him. I did
THIS more times than I like admitting. Fortunately, the labels saved me. Taking a few overall photos of an amp before you start disassembling it may prove useful.
Internally, there are a couple of features that you may want to photograph. The first is the transistor clips/clamps. In some instances, they will only fit properly in the original configuration but can be installed with other configurations. If you perform enough repairs, you'll see quite a few amps with numbers on the clamps. I've numbered clamps and even
marked heatsinks for clamps that would be difficult to mark but photographing is a cleaner way to do it.
The screws are another item. There will be instances where screws that look different (chrome/dull gray/black) will be used in the same numbers and will fit in various locations. Again, some people get upset if their amps are not exactly the same (physically) when returned to them. I know, they shouldn't be going back into it but some will. Some people have spent hours looking at their beloved amps and are finicky about slight changes. Some will consider the amp improperly reassembled if it's not precisely the same.
You can use
Tamper Evident labels and tell them that the warranty will be void if the labels are removed but I'm not sure if you can legally void the warranty if they do break the seals. I doubt that many people would take you to court but with social media, they may be able to damage your reputation.
Digital photos cost nearly nothing, now that storage drives are dirt-cheap ($35 for an SSD drive that will hold more photos than you're likely to ever take). Save to one drive and backup all files to a second drive at least once a month. Keep the second backup in a different location than the first, in case of fire or theft. If you lose one copy of the files, back it up immediately. If you can justify the cost of (private) cloud storage, that may be an option for the backup. You want at least one copy of the photos stored locally because (if you're like me), you'll reference them regularly and local access is MUCH faster than with cloud-based storage. It also give you options for the image viewer
(Irfanview, recommended).
My preferred backup storage is a SATA SSD drive. The main storage drive is plugged into a SATA port on my motherboard. To connect externally to a backup drive, I have two options, either a USB to SATA cloning cable or a docking station. Plugged into USB 3.0 (the fastest I have), the transfers are fast. You can backup to a USB flash drive but they can be unreliable and slow.
It may be difficult to, initially, justify the cost of storing the images but I have been taking/collecting photos... for 20+ years and a cost of less than $100 is a bargain to protect all of those photos... not to mention the great resource they are in finding the values of burned/missing parts. The backups are also for all of the service literature (diagrams, service manuals, etc.) I've collected over the years, much of which may no longer be available.
While photo storage is very important, the storage of notes (particularly of voltages taken from the various circuit points in a
working amplifier), is important because they are a valuable resource. This means that they should be protected, as well. These take up virtually no space in text format (best format because it allows them to be easily edited) but even as a photo/scan produced from a handwritten page, they don't require a lot of storage space. If you don't have a secondary storage drive (an inexpensive
[Wal-mart, less than $10] USB drive is perfectly suitable), send the notes to yourself in an email and make a dedicated folder in your email account in which to save the note files. Some may choose to store files in their phones but unless you have the phone sync'd with a cloud storage, I wouldn't recommend it since phones get lost/stolen and you wouldn't want to lose the files.
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.
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.
The twisting/pushing/pulling test will be used often (ideally, several times on
every amp from the time it's first back to functioning and again just before the top/bottom cover is installed). Don't forget it. It can save valuable time and prevent embarrassing boomerang amplifier repairs. See TT5,
item #1 for more on this.
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.
In general, when you see the term
rail voltage, it's a voltage (or pair of voltages,
±)
† produced by the amplifier's switching power supply (the part with the large
toroidal,
† wire-wound transformer). This is (generally)
† the
source of power for the output transistors. The
output transistors drive voltage/power to the speakers. In most amplifiers, this rail voltage is the greatest voltage
† (positive and negative) and can produce the highest current of all of the voltages generated by the power supply.
†For the majority of amplifiers, the rail voltage will have positive and negative components (above and below ground/0v). For some amplifiers, like those in many class D amplifiers, there will only be a positive rail voltage for the output transistors. There will likely be
±supply voltage for the preamp components but only positive rail voltage for the output transistors.
†This (the use of toroidal
[doughnut shaped] transformers), like so many things, is not absolute. Many transformers used by Japanese, Brazilian and even American manufactures (like Zapco) are
square transformers (cheaper to produce in large numbers).
†'Generally' because you can use the term for voltages other than the main (output) supply rails. For example, you may see the term
±15v rails. This would be the regulated,
low-voltage supply that's typically used for the various preamp-level components.
Yet another set of rails... The
±15v voltage regulators may have their own set of rails at approximately
±20-25v. These are often produced because the voltage regulators often have a limit to their acceptable input voltage so their input can't be taken from the full output transistor rail voltage. The lower voltage rails are often produced by a dedicated set of windings on the power transformer.
†In some amplifiers, there is a low-current, higher
_than
_rail driver voltage that's produced that's approximately 10
-15v above the main rail voltage. This allows the output transistors to be driven more efficiently (delivering closer to 100% of the rail voltage). In those amplifiers, the driver voltage would technically be greater than the main rail voltage.
There will be amps that have a fault that causes it to drive significant (well over 1v) DC voltage to the speaker. This isn't simple DC offset, especially when rail voltage (30, 40, 50v, or more) is driven to the speaker. This can be a fire hazard and can destroy expensive speaker(s) connected to the faulty channel. If the fault is intermittent, the amp cannot be used until positively repaired. If you have to repair it, be
absolutely sure that you find the intermittent problem.
The same applies to an intermittently shorted transformer that's driving B+ (12v) to the RCA shields.
You were warned about this previously on this page in the note about grounded shields (which was entirely ignored/dismissed). If you refuse to make and use the simple adapter, you had better have plenty of insurance, an LLC or both.
If you can't
definitively find the fault,
do not accept payment for repair. Tell the owner that it's
not repaired and would be dangerous to use it as it is. This is
critically important if you want to limit liability. If the problem reoccurs and destroys speakers or causes a fire, you could be held liable. Find the fault or
return it to the owner at
no charge. If you charged a deposit,
return that as well. You want to make sure that the owner can't say that he paid you to do anything and that what you were paid for resulted in any type of loss. People are litigious
(some, enthusiastically so). Don't give them a chance to think to themselves... ka-ching (or is it, cha-ching) for
anything you do.
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.
When working on amps, you'll likely have lots of wires connected to the amp. Since it's not really practical to have all of the wires cut to the shortest length possible (because many have to work with multiple amp models), it's easy to become entangled in the wires (they can even get caught in the chair and will be pulled when the chair is rotated). If this happens and you get up to go get a part or look up a datasheet (or for any other reason), you must be extremely careful not to pull the amp off of the bench. Doing so can do extensive damage. When getting up, do so slowly and make sure that you are clear of all wires before walking away. If the work-surface is more rubbery than slick (laminated countertop material...), this is less likely to happen but the rubbery surface won't eliminate the risk of pulling items off of the bench.
In a similar way, I've seen people disconnect an amp (or so they thought) and when they begin to walk away, the amp is nearly pulled out of their hands or something is pulled off of the bench when the wires (that they 'thought' were disconnected) tighten up. Again, Be careful and take your time. This may seem obvious but when you're deep-in-thought, learning something new and you're distracted, it's easy to make simple mistakes.
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.
-
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.
Note:
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.
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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.
You'll see the phrase 'excessive current draw' used often. It means that an amplifier is drawing more current from the 12v DC power source than it should (generally at idle, no load and no input signal). For most small to medium sized amplifiers, the current draw at idle is 0.5-2 amps. For larger amplifiers, the current draw can be as high as 5 amps at idle. Of course, when you connect a load (speaker) to the amplifier and drive signal into it, the current draw will increase as the amplifier produces power into the load. If you power up an amplifier and the amp meter on your 12v power supply swings to the maximum current and doesn't IMMEDIATELY fall back to approximately 1-2 amps of current (for small to medium sized amplifiers), the amplifier is drawing excessive current and you should not apply power again unless you do so through a current limiter (to be covered later) or until you find and repair the fault that's causing the excessive current draw. It's important that you are able to quickly switch off (or disconnect) the 12v power supply if there is a problem.
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