This site has supported itself for about 20 years but now it's no longer doing so. As of the end of the year, it's likely going to go offline. For those who may own a car audio related business and may want to advertise on this site, email me if you want to have your ads on the site. They will be the only ads except for (maybe) the car amplifier repair tutorial ad. The ads will be in the form of a static (not animated) 800*100 banners that will be hard coded into the site (can't be automatically blocked by standard adblockers). There will be no other competing ads. I'm taking bids until the end of the year. Selection will be based on the bid as well as the suitability of the business. If no bids are sufficient, the site will likely come down. I don't want to sell the site or domain.
If you have a problem with some graphics showing up as large open spaces, empty or black boxes, right-click the link in the directory for the page you're viewing and open the page in a new tab. This will resolve most/all of those issues. Setting the font size at 1 step larger than the default will also help if you want to view the site in it's original format.
Many people need help repairing their amplifiers but are afraid to ask for help because they don't want to sound like an idiot (asking stupid questions, etc...). The information on this page will help prevent asking questions that may be deemed as stupid. 'Stupid' questions are generally those asked by someone without enough knowledge about the subject to ask meaningful/useful questions. If you take the time to read this page in a manner that will allow you to absorb most (or all) of the information here (expect to spend at least one full hour reading and re-reading -- maybe a bit more if you're struggling to understand it), you will learn the proper terminology and the basic operation of an amplifier. In most instances, most of your questions will be answered here and you will only need a bit of clarification for your specific amplifier.
To help the page load more quickly and to save bandwidth, many of the photos will be loaded from links. When you're done viewing the photo, close the window. If you leave it open and return to this page, the next photo may load in the background window and it may appear as if the link isn't working. The green links are photos. Most of the other links are to web pages on this site. If you're serious about learning to do this type of work, you should follow the links and read the pages from top to bottom. There are too many people who claim to be serious about amplifier repair and fail to read EVERY linked page. Those with an honest desire to learn the material, not just reading to say that they have done so, will read and re-read the linked pages until they truly understand the material.
Schematic Diagrams for Amplifiers:
Be Pro-active if you want to Learn to Repair Amplifiers:
Basic Amplifier Layout:
If you think you'd like to be an electronics technician, you'll have to decide whether you want to understand the circuits, troubleshoot the problem and replace only the components (or group of components) that are necessary to repair the amplifier. Most have a low opinion of mechanics that are 'parts changers'. Because they don't understand the operation of the various components in the vehicle well enough to troubleshoot properly, they make a guess as to what needs to be replaced and continue until they get lucky and find the defective part. This is time consuming and expensive. If you want to be a knowledgeable technician, you can learn on your own but that takes a lot of trial and error. The cost of the tutorial below is far less than the cost of the components that most rookie techs will destroy in their first few repairs.
On this page, you will see the terms below many times. The following section is to help prevent confusion and provide additional information. For more detailed information, follow the links provided.
When checking semiconductors, you will use a multimeter. To be able to do any troubleshooting, you need to know what your meter is telling you. Try the following in ohms AND diode test modes:
There are several types of protection circuits in amplifiers. The most common are over-current and thermal. The over-current protection is supposed to protect the output transistors. Sometimes it doesn't work well enough to prevent the failure of the output transistors but it will work well enough to shut the supply down before the power supply FETs are destroyed. If the amp remains in protect mode, goes into protect mode or blows the fuse as soon as the remote voltage is applied, shorted output transistors are almost certainly the cause.
If the fuse protecting the amp is too large, if the protection circuit doesn't respond quickly enough or if the power supply is poorly designed, the power supply transistors may fail. If you see a lot of black soot on the power supply transistors (near the power transformer), the power supply transistors have failed. Soot on the board doesn't necessarily mean the transistors have failed. Sometimes, technicians don't clean up the mess from a previous failure.
Transistor Failure/Checking Transistors:
Right-click to zoom in.
When checking power transistors in the power supply or the audio section of an amplifier, you look for shorts between the legs. If you get a reading of near zero ohms with any combination of the meter probes across the legs of any individual transistor, the transistor is likely shorted (or is in parallel with a shorted component).
If you check 3-legged rectifiers in the board, you'll find a short between the outer legs (for the most common 3- legged rectifiers). The short you're reading is actually the windings of the power transformer. If there is no short between the center and outer legs of the rectifier, it's likely OK. THIS page tells you how to check the most common transistors. Scroll down to the section labeled "Checking Field Effect Transistors". The tests for BJTs are farther down the page. THIS page shows a slightly different way to check transistors and has applets to allow you to send me or post screen caps of the readings from transistors (click the black bar at the right of the applet for instructions).
When power supply transistors fail dramatically (smoke, flames, soot blown out onto the board...), they generally short internally (all terminals shorted together) but the high current flow causes the third leg to fuse open. Sometimes, there is no visible damage but the third terminal opens internally. In these instances, you can see a direct short between the first and second terminals.
This page is a VERY basic introduction into car audio amplifier repair. If you're interested in learning more about troubleshooting, the commonly used components in car amplifiers and the way they work, you may be interested in the full version of the repair tutorial. The full version also contains many examples of common problems with many of the most common amplifiers. This includes tips for common problems that may not be apparent when replacing blown components which can result in premature failure of the amplifier. If you're interested in learning more, click . As of now, the 'downloadable' version of the tutorial is $20 less than the DVD version.
In most amplifiers, you'll find groups of parallel components. The components are used in groups because a single component can't handle the stress. When in parallel groups, the components MUST have virtually identical characteristics. If one or more are just slightly different, the load will not be shared equally and it can cause the amp to fail prematurely. When one component in a parallel group fails, all in the group MUST be replaced for optimum reliability. Even if the replacement part has the identical part number, it will not be exactly the same as the original parts and won't share the load properly. The date or production code is a good way to identify parts that are very similar. Parts with the same date code will have identical markings printed/etched on their face. If there is any difference in the markings, they may not be well matched. If the parts have the same date code, they are going to be closely matched. Generally, when you order parts, you get the same date code but that's not always the case. If you buy 6 parts and the distributor has them prepackaged in packs of 1s, 5s, 10s, you will get one pack of 5 and one single pack. These are unlikely to have the same date code. If you are not ordering a full stick of parts (50pcs/stick for TO-220 parts), order more than you need so you can be relatively sure you will get enough matched parts.
The following image shows the parallel components for an audio amplifier. The configuration will vary from amp to amp but the basic layout of the parallel components will be similar to what you see here. For switching power supply components, there are no emitter resistors. This makes the matching of the components that much more critical.
Datasheets are documents that tell you virtually everything about a particular component (including pin configuration, the pin numbering scheme and the names of the individual terminals -- particularly important for transistors). For a single transistor, they can be 10+ pages long. For ICs (Integrated Circuits -- chips), they can be 20+ pages long. Datasheets can be used to find the specifications like current capacity and maximum operating voltage. This is handy when you need to substitute a part that's no longer available. If you need a datasheet, use Google and search for 'datasheet' and enter the part number of the component. If you use Octopart, you don't need to enter the term 'datasheet'. A link to the datasheet will be provided when the results for the search are returned. If you use Mouser or Digi-Key for parts, when you look up a part, a link will be provided for the datasheet on the information page for the part.
The following are 3 datasheets for commonly used components.
In general, it's best if you use replacement parts that are the same exact part number as the original. In some cases, it's OK to make a substitution if the replacement has better specifications than the originals. Until you know an amplifier very well, use the original parts. In class D amplifiers, you should not make any substitutions. In some cases, the new replacements will vary enough from the originals that the same part number component will not work properly.
Surface mount components make a repair slightly more difficult. They are typically smaller and the pads can be damaged easily if you're not careful. Using good equipment and good technique, you will be able to replace them easily. In THIS photo, you can see several surface mount resistors and a surface mount semiconductor (a diode). These commonly burn when the power supply fails. To remove them, you apply new solder to both sides, heat one end for 2-3 seconds and then move the iron to the other side. When the solder melts, the resistor will slide off of the pads (if it's done quickly enough that the other side hasn't had time to cool).
You read the value off of the surface mount resistors just as you would for resistors that use color codes (except you don't have to remember the colors). The resistors marked 680 are 68 ohms. The resistor marked 101 is 100 ohms. Refer to the Resistors page for more information on reading resistor values.
As with any type of work, it's easier to do a job with good quality tools. The following are some of my suggestions.
For those who will do a lot of repairs, you will need a sturdy set of shelves. The following shelving unit is one that I built to for my shop. If you're interested on building it, you can find the 3D model and information for the software to view it on one of my sites. Go to page 10a in the directory of the site.
Gate Drive Signal:
The driver transistors drive the square wave signal into the gate resistors (the resistors connected to the gate terminal of the power supply FETs). In the photo, resistors R924, R928 and R934 are the gate resistors for 1 of the 2 banks of power supply FETs (3 FETs per bank in this amp). In most amplifiers, the value of the gate resistors is between 27 and 100 ohms. These are a bit higher at 120 ohms. It's common for the gate resistors to fail when the power supply transistors fail. As I mentioned before, the gate often shorts to the drain (terminals 1 and 2 of the FET -- look at the IRF1010EZ datasheet, page 9). When this happens, the drivers have to work against the internal short of the FET to try to pull the gate voltage down. It's essentially impossible because the terminals are fused-together internally and terminal 2 is essentially connected directly to the B+ terminal of the amp. If the drivers are tough, the gate resistors will fail. if the drivers can't handle the current (when trying to pull the gate voltage down), they will fail (unless the gate resistors fail first).
Rectification and Filtering:
When troubleshooting an amplifier, you must confirm that the power supply is producing both positive AND negative rail voltage. There are a few amps that don't have negative rail voltage. The class D amps based on the HIP4080 driver IC will only have positive rail voltage. Lower voltage (±15v) will be produced for the preamp section of the amp but the power amplifier section doesn't use a negative power supply. 'Chip amps' which operate off of the B+ voltage (like the internal amplifier of a head unit) do not have a switching power supply and will not produce a negative power supply voltage.
Linear Voltage Regulators:
You must confirm that the pre-amp op-amps have both positive and negative supply voltage. You will find regulated voltage from ±10v to ±18v in amplifiers. ±15 is the most common voltage for the op-amps.
Getting a Clean Input Signal:
Power Amplifier Section:
In most amplifiers, the differential amplifier is driven into a voltage amplifier. A differential amplifier can't swing its output fully from rail to rail but the voltage amplifier can (or at least get very close to the rails). The voltage amplifier drives the driver transistors and the driver transistors (2SC3421 and 2SA1358) drive the output transistors. The output transistors drive the speakers.
Sometimes, when the output transistors fail, they will cause the drivers to fail. If you're repairing an amplifier that has blown output transistors, you should check the driver transistors also.
In the driver transistor photo, you can see a small transistor between the output transistors on the heatsink. This is a bias compensating transistor. Previously, I mentioned that the dual transistor package insured that the two transistors maintained the same temperature. If the transistors are not at the same temperature, their electrical characteristics will not match (even if they are otherwise identical). The same is true for the output transistors. If you set up an output section to where there is always a tiny current flowing through the transistors (class AB operation), this current will change as the temperature of the transistors changes. To compensate for the changes in the electrical characteristics of the output transistors, a bias compensation circuit is used. The small bias compensation transistor prevents the bias current from changing significantly. Without it, the output current would increase significantly as the temperature of the output transistors increased.
Many times, there is a bias adjustment potentiometer. It allows you to set the bias/idle current of the output transistors. If the bias is set too high, the outputs will run too hot and be more likely to fail. If set too low, the output could be distorted. There have been many instances where someone has gone into an amplifier and turned the bias pot up (thinking that they were increasing the power output of the amp). This caused the amp to fail. Unless a potentiometer is accessible from the outside of the amplifier, you should not turn it unless you know what it is. Having the bias current set too high is like having the idle setting on your car's engine set to 3000 RPMs instead of 750 RPMs.
Previously, we looked a scenario where the amp would try to power up but would go into protect or blow a fuse. Troubleshooting a dead amplifier is different.
When an amplifier will not power up, you have to confirm that you have ~12v across the B+ and ground terminals. You also must check the fuses (all must be intact). If those check out, you need to open the amp and look for signs of damage. If there is no visible damage, you need to begin checking voltage on various points. Connect your black meter probe to the chassis ground terminal of the amplifier. Measure the voltage on the center leg of the power supply FETs. It should be at or near 12v. If that's as it should be, check the voltage on each pin of the TL594 (or whatever driver IC the amp uses). Using the datasheet, determine if the IC is operating properly. Each IC has various input pins (to error amps or other internal control circuits). Determine if the IC is operating but being shut down or if the IC isn't operating properly. If the IC has the correct voltage on the 5v reg and the correct voltage on the sawtooth waveform pin, the IC is likely OK. The following is a list of basic checks:
Protection circuits are beyond the scope of this basic troubleshooting guide but I'll provide a basic introduction to them. In general, protection circuits are designed to prevent damage to the amplifier and, in some cases, they prevent damage to the speakers.
Any of these can shut the amp down. If there are no dedicated indicators to tell you which fault has caused the shutdown, you must determine which fault is causing the shutdown and then find the defective components. With a schematic, it's generally not too difficult. Without a schematic (many manufacturers won't provide schematics), it can be much tougher.
(shows some signs of life)
If you're asking for help with a repair and you include answers to the following questions in the initial email/post, it will generally greatly speed up the process.
In most amplifiers, you'll find both positive and negative rail voltage. If you have one but not the other and the amp isn't a class D amp (some class D amps only use positive rail voltage), you need to determine why you don't have both positive and negative rail voltage. If you don't have both positive and negative regulated voltage on the power supply pins of the audio op-amps, you need to trace back the circuit to the regulators to see why you don't have the proper regulated voltage (generally ±15v). Many times, a distorted or intermittent channel is due to nothing more than a dirty contact in a potentiometer or a switch. Sometimes it's simply caused by having the switch between positions.
The power LED is not a good indicator of the condition of an amplifier. Just because the LED is lit, that doesn't mean the amp is operating. In many cases, it's simply an indication that the amp has B+ and remote voltage. In some amplifiers, the power LED will be lit with only the remote voltage applied (B+ isn't required). Amps like those made by Sony may have all green lights lit even if an amplifier has a blown power supply. Amps like those made by Rockford, must have a working power supply for the power LED to be lit.
In many amplifiers, the protection LED will only light if the power supply is working and the audio circuit trips one of the protection circuits (over-current/DC offset). If the power supply is blown, it's generally not possible for the audio circuit to trip the protection circuit and therefore the protection LED will not light.
In virtually all amplifiers, you will find 'bipolar transistors' (BJTs). To check them, you need to understand their basic construction (as it applies here). In most BJTs, you'll have nothing more than two diodes. As you know, a standard diode passes current in only one direction. When checking them with a multimeter set to 'diode check', you should find that the meter reads ~0.6v in one direction and reads as an open circuit when the probes are reversed. You should find the same thing when checking bipolar transistors. Looking at the two images below, you can see how the diodes are orientated in the package. Note the locations of the base, collector and emitter. The placement of the probes on the B, C and E are important. The pin-out of the transistors can have the B, C and E in any of the 3 positions. You need to download the datasheet for the transistor to determine the pin configuration (B, C, E). For most power transistors in the TO-220 case/package (below) or the larger cases, the pin configuration is virtually always BCE.
In these two images, you see that the forward voltage drop is 0.6v. In all other combinations of probe placement, the meter should read the same as when the probes are open (not in contact with anything). Any other reading means that the transistor is defective. Understand that the 0.6v is simply a common value. Anything close to 0.6v with no reverse leakage (current flowing through the internal diodes backwards) means the transistor is likely OK.
If you need help checking transistors, fill in THIS form, produce a screen capture image and email it to me. The case style of your transistor isn't important when using this form. Simply have the text/part number facing you and the legs down. Don't forget to enter the transistor's part number in the form. You need to pull the transistors from the board for definitive testing/results. BEFORE entering all of the values, make sure that you can produce the screen capture.
7mm Set Screws for Terminal Blocks:
If you've made it this far, and you're still interested in doing this type of work, read the first 12 chapters of the site until you understand them completely. Then read the following chapters (some of these are links previously seen in the text above):
The tutorial I sell (click banner below) has MUCH more detailed information and covers a much wider range of amplifiers and problems. If you're interested in doing this as a side-line job, the tutorial will be a great help. If you're an engineering student, you'll learn a lot about electronic components but you won't get much information about the way those components are used in real world products. The tutorial will help fill in large gaps that won't be filled by college courses.
Reputable, Reliable Distributors:
It may seem a bit strange that there is photographic information on an amplifier repair page but there are thousands of amplifiers on the market that I've never seen and will never have in my shop. Photos, especially good quality photos, allow me to see the amp in question and will often make it possible to help the owner get it repaired.
If, after reading this section, you would like more information on macro-photography, you may want to visit my Basic Macro Photography Tutorial site.
It's not necessary to have an expensive camera or accessories to take decent photos. If the first few (or 10, 20, 50...) photos you take aren't very good, keep trying. If you don't have the patience required to get a good photo, you certainly don't have the patience needed to repair your amplifier. Please don't submit cell phone images. As of this time, most are useless for this purpose. I'm sure that in a few years they will get better but they're not there yet (mid 2011). If you want to compare your cell phone images to a 7 year old, lowly 2MP camera (Nikon Coolpix 2200), try to match the quality of the following image. The reason I mention cell phone images (and provide a sample to which they can be compared) is because of the rude responses that I've gotten from people who are offended when I tell them that their iPhone (or whatever phone) images aren't good enough. If you don't have a digital camera, you probably know someone who will let you borrow their camera.
If you're going to buy a camera, it's generally best to buy one that uses commonly available, inexpensive batteries (AA preferred). Also make sure that, if the camera requires the use of proprietary cables, the cables are included or are available relatively inexpensively. If it requires a memory card, try to buy a camera that either includes the card or uses a card that you already own. If you're going to buy a camera, go to a site like the Imaging-Resource and look at the sample images (particularly the macro images) to see what the camera can do. Viewing the sample images can also be helpful if you own a camera and cannot get acceptable images because it allows you to see what the camera is capable of. Many times I'll get a photo where part of the amp is in focus but the relevant part is not. Look at the photo before you send it. If you see that some of the image is in focus, do whatever you need to do to shift the area of focus to the relevant part. If you send me a poor quality image, I'll look at the EXIF data. If I find images that are significantly better than what you took with your camera, it's unlikely that you will get a response. If you can't take the time to get the most out of your camera, I'll assume that your question probably isn't important enough to be answered.
Macro or Normal Mode:
Angle at which Photo is Taken:
Flash or No-Flash:
Auto or Manual:
Nikon Coolpix 2200:
As you can see, a 2MP camera can take relatively good quality photos. Click on the image to view it in a new window. If you're using Firefox or Chrome, click on the image after it's loaded to view it at full resolution. This camera cost only about $20 (plus shipping) on eBay. If you buy a camera like this or a similar one, be aware that most have broken battery door latches. Read the description and look at the auction photos carefully before buying one.
The following photo was taken outdoors with a heavy overcast.
The photo below was taken with the camera body parallel to the board. As you can see it's not nearly as good as the one above. Basically, the only difference was the angle at which the photo was taken. The components are all in focus in the image below but the bright reflection is distracting and fatiguing, especially if you have to look at multiple photos or if you have to study the photo for more than a few seconds.
Many of the visitors of this site claim that they want to learn to do repair work for profit. If you have no desire to work towards taking the very best photos that your camera can produce, it likely means that you're not a quality oriented person and should not be doing work for others.
For those who read this and see something that they've done and think I'm singling them out, rest assured that I'm not. Nothing is here because it happened one time. If it's here I've seen it so many times that it's gotten annoying and this is an attempt to prevent seeing it again. When asking for help, take time to think about the problem and include all information that you think is relevant. Putting forth a bit of extra effort could mean the difference between getting the desired answer in a few minutes or having it take a few days (or longer).
Reducing Variables When Troubleshooting:
Do you best to make the photos you post as good/useful as they can be. Post at relatively high resolution (at least 800 pixels wide). Most cameras produce images at least 2000 pixels wide so you probably won't have an excuse not to post decent size images. When posting the image, orient the camera so that the amp is displayed lengthwise through the longest axis of the frame of the camera. The next image is what NOT to post. Not only is the image too small, it doesn't make the most of the frame of the camera.
This next image is better but there is a limit to the size of the image file that can be posted. This image has a lot of useless space. That needs to be cropped. This can be done with your favorite software. If you don't have favorite software, something like can be used. To crop, drag a box around the part of the image you want to keep, hit ctrl-y and save. The link is to the bare Irfanview exe file (zipped). If you unzip it and double-click it, the program will open (no need to install it).
The next image shows what the cropped image looks like. If you post a really large image, it will be displayed as a smaller thumbnail. When you click on it, the larger version will be displayed (as you can do with the image below). These are the most useful, especially when the person helping you isn't familiar with the amp.
Proper Grammar and Spelling:
It may seem like I'm being unreasonable asking for this but this is technical and the language needs to be precise so I don't have to ask for clarification of everything you send me. As a general rule, you should attempt to write at approximately the same level as the person with whom you're corresponding. If you're in a forum where there is nothing but slang, then it's appropriate for you to reply that way. If the person corresponding with you is taking the time to use proper grammar, punctuation, capitalization and paragraph breaks, you should do the same. I'm willing to help just about anyone (free of charge) but you have to do your best to help me to help you. If this is too much to ask, please look for help elsewhere. If you're from somewhere other than the US and/or English isn't your native language, do your best and I'll try to help.
There will be times when a mistake (slipped probes, overheating components that fail...) will cause components to burn. If a component burns beyond recognition and no one can tell you what it was, the amp may have to be sent back to the manufacturer for repair. Before you do anything to the amp, remove the cover and take photos of all of the components from all angles in good light. Check the photos on a laptop or desktop computer (large, high-quality monitor) so you can confirm that they're in focus. Save a copy to the computer. When posting on the forum, post a single, good quality photo of the entire board. Many amps are clones of other amps. If someone isn't familiar with the make/model amp you have, they may be familiar with a clone of the amp and will be able to help you.
If you ask me for help and use chatspeak, LEET or truncated/abbreviated words (ur for you are, str8 for straight, etc...), don't expect me to reply. If I do reply, it will likely be to ask you to re-submit the question, written properly. If you're not intelligent enough to ask properly, you're unlikely to be intelligent enough to complete the repair. Many of the replies require 10 minutes to an hour to find the answer. If you can't take the few seconds that it takes to spell out words, you shouldn't expect anyone to spend time trying to help you.
If you're someone with a legitimate learning disability and cannot use proper grammar for that reason, you can still use capital letters and periods. The spell-checker in your browser will take of spelling errors. It will at least show me that you're trying.
Circuit Board Designations:
In the following image, you can see that virtually all of the components have a circuit board designation. The prefix tells you what type of component it is (R - resistor, Q - transistor, D - diode, C - capacitor...). R147 is the pink resistor. R52 is the large gray resistor. Q21 and Q9 are transistors. C37 is a capacitor.
While I have a lot of photos and schematic diagrams (been collecting them for quite a long time), I don't have information on every amp. In some instances, you'll need to supply a reasonably good quality photo so that I can read the circuit board designations and make sense of what you're asking. The photo section on this page is provided to help you get the best possible photos. For those who don't have a camera that can take good quality photos (only have cell phone or web cam), you can use a lower quality image and mark up the photo in Irfanview, Microsoft Paint (free with Windows) or your favorite photo editing software.
Many times, a schematic diagram or photos from an amp 'similar' to the one you have will be used for a reference. If you believe that something doesn't seem quite the same on your amp, ask questions or ask for clarification.
Reference Point when Measuring Voltage:
When measuring most voltages, you will place the black meter probe on the amplifier's primary ground (the amplifier's main ground terminal). You'll then place the red meter probe on the point where you need to measure the voltage. Use the amplifier's primary ground for the reference point (black probe) unless otherwise instructed (for those asking for help on either the car audio forum at DIYAudio.com or via email). In some instances, you'll need to use the secondary ground as the reference. If that's the case, I'll generally tell you what point to use. The non-bridging speaker terminals (the speaker terminals that are NOT used when the amp is bridged) are often the reference point (black probe placed there) for the secondary ground.
As an example, if you're measuring the voltage on the power supply driver IC (TL494, TL594, SG3525...), you'd place the black probe on the amplifier's ground terminal and touch the probe alternately to each of the pins of the driver IC. If you're asking for help and I need these voltages, I'll generally give a list for you to fill in the blanks. If it's via email, simply fill in the voltages after each pin number. If it's on the forum, copy and past the list. The list is precisely as it is for a reason. There is a blank space after each pin number to make it easier to read. If the space doesn't get copied, it's simple enough to add a space before you type the value. There is a colon after each pin number so that the person filling in the blanks doesn't use hyphens (which can be mistaken for a negative sign). There is a reminder to list the IC number (circuit board designation) if there is a chance that it will be confused with another IC. This is generally only an issue when you're listing the voltages from multiple similar ICs.
Here is an example:
IC# << insert IC circuit board designation here
THIS is a plain text file (open with Windows Notepad) that has no formatting and retains the spaces as they should be. Right-click and save to your computer if your browser opens it and adds formatting, Copy and paste the number of pins for the IC you're measuring the voltage on.
Voltage 'Across' or Voltage 'On' a Component Terminal:
Don't Forget the Units!:
If you look closely at the first value, you can see that there is a 'k' in front of the symbol for ohms. In the second one there is no 'k' in front of the symbol for ohms.
Don't Try to Seem like You Know what You're Talking About if You Don't:
Those who don't understand that intelligent people can be ignorant, don't know the definition of ignorant. Ignorant means that you don't know. We're all ignorant of something.
Not Everything is a MOSFET:
Datasheets for Replacement Parts:
Transistor Type vs Function:
State ALL Work Previously Done to the Amp:
Don't Reinstall/Remove Parts Without Letting Others Know:
Don't Break an Email Thread/Chain:
If you have a thread or email chain that you've started for one amp, don't ask questions about another amp in that chain/thread. Start a new chain/thread and include the make/model of the amp in the subject line of the message. Each time you start a different repair, start a new chain/thread.
On the forums, do not ask questions about your amp in a repair thread started by someone else with a similar amp. Start your own thread. It gets very confusing, especially if the original poster has additional questions about their amp. If you're not intelligent enough to start a new thread, there's a pretty good chance that you're not intelligent enough to repair your own amp.
Problems Concerning Noise or Distortion:
Distortion makes the output less clear, harder to understand. If your amp only distorts as the output increases (but well before you think it should), you need to confirm that the DC voltage across the B+ and ground terminals of the amp (multimeter probes placed directly on the metal part of the B+ and ground terminals on the amp) is remaining at or above 12v. If it's dropping lower, that could be part of the problem and you need to determine why it's dropping.
Is it distorted at all output levels or only at higher output levels?
Is only one channel distorted or are multiple channels distorted?
Does changing the position of any of the controls make a difference in the quality of the output? When checking this, you need to have a speaker connected to the channel that's defective, listening carefully while operating all controls through their entire range. If the audio becomes clear in one position (even intermittently), you need to include that bit of information when you ask for help.
You also need to be specific about it's relative loudness of the noise. Is it barely audible (ear needs to be almost on the speaker to hear it)? Is it moderately loud to where it would be difficult to hold a conversation over it? Is it so loud that it absolutely overwhelms any audio, no matter the volume level?
Is the noise being produced only by the internal components of the amplifier or is the noise audible through the speaker as well? Many amplifier produce significant noise from the various transformers and inductors and it is often not a problem that needs to be or can be resolved. If the noise is not entering the audio signal and would not be audible when the amp was being used normally (all covers on, amp in trunk or in amp rack...), it's probably not something that you need to be concerned with. When asking for help, be sure to note whether the noise is audible or not in the speakers.
Does the noise vary with a change in the position of any of the controls on the amp?
Does the noise go away when no signal source is connected?
Does the noise vary with the level on the signal source?
Are you using a battery-powered signal source (ipod, etc...)?
Are you using a test speaker appropriate for the amp that you're repairing? If you're repairing a multi-thousand watt class D amp and are using a full range speaker with efficient tweeters and hear a hiss, that doesn't necessarily mean that there is a problem. Some class D amps are noisy. If you were to connect a subwoofer, would the installed amp produce enough noise to be audible?
As a side note...
List of Test Equipment:
An oscilloscope isn't absolutely required for all repairs but it makes it easier to help with repairs that involve distorted output. You will be asked to post or email a photo of the distorted waveform. When you take the photo, you should set the camera so that it doesn't use the flash. It's not important that the face of the scope be well lit when all that's needed is a photo of the displayed waveform. You'll need to use a sine-wave for the audio source. You can download the following test tones. You'll need to either burn them to a CD or copy them to your digital audio source (MP3player, ipod...). The 100Hz is most commonly used.
If you're not completely familiar with the use of an oscilloscope, you need to read the oscilloscope page of this site (#73 in the directory). You need to read EVERYTHING on that page but pay special attention to the section labeled Best Initial Settings. Read that section at least twice (once before setting the controls and once after setting the controls to confirm that they're as they should be).
Final Word for this Section:
There have been a lot of questions about the type of scope necessary to do this type of work. Many people are under the impression that they need an expensive 100MHz scope to troubleshoot audio circuits. That's simply not the case. Below, you can see two different scopes. The first one is a Tektronix 2230 digital storage scope rated for 100MHz. The second photo is the same signal displayed on a Tektronix 5110 oscilloscope rated for 2MHz (not a misprint, 2MHz). Although the 2230 has slightly better resolution, the 5110 has good enough resolution for virtually any problem that you'll encounter. The signal is a 160kHz square wave. This is typically the highest frequency you'll find in the audio section of most class D amps. Some full range class D (T) amps operate at higher frequencies but those amps are not common. Even those amps that operate at higher frequencies operate well below 1MHz.
If you look closely, you can see ripple on the top and bottom of the waveform. This is at a much higher frequency than that of the square wave but it can still be seen in the 5110 display.
Some people will argue that a 2MHz scope will not be able to resolve tiny high frequency glitches. That's true to some degree but that's not really a concern with most audio problems. I don't want you to think that I'm telling everyone to go out and buy a 2MHz scope. This is simply to show that it doesn't take a 100MHz scope to display the types of signals found in car audio amplifiers. If you can get a good deal on a 15MHz or 20MHz scope, don't pass it up because you don't think it's up to the task. Virtually any scope with a triggered sweep and in good working order will suffice.
If you're looking to buy a scope on eBay, email the auction numbers to me and I'll try to help you get one that is in good working order.
When buying semiconductors, you should only buy from reputable distributors. There are quite a few counterfeit/fake components on the market. Sometimes, the counterfeiter will buy cheap components and re-mark them. Others could simply be manufactured with very low standards. If you have an amp that fails repeatedly after repairing it and you suspect that the transistors may be fakes, break open the package and compare the size of the silicon die to those in the following photos. If your transistors look like the die has been glued to the tab or the die is significantly smaller than the ones in the photos below (for the same part/manufacturer), you may have counterfeit parts. You can send the parts to the manufacturer and they will be able to determine if the components are genuine or counterfeit. I believe that the transistors below are genuine components unless otherwise noted.
Other sites that have information about counterfeit semiconductors:
I have received more requests for the service manual for this amp than any other. The problem is virtually always the same. Q4901 has failed or the amp is non-functional with no blown power transistors (output or power supply). The problem is generally Q4901. This transistor is the voltage regulator for the drive circuit for the class D amplifier circuit. When it fails, the drive circuit has no supply voltage so it cannot function. If you're lucky, it has failed alone and replacing it is all you need to do. The original transistor can be sourced from PacParts.com. The can be used as a substitute but it needs to have a suitable electrical insulator (mica, Kapton...) installed between the transistor and the heatsink.
The transistor fails because it runs too hot. That's because it's being asked to dissipate too much power (in the form of heat). To make matters worse, Alpine assembled the amp without applying heatsink compound under the transistor. Yet another problem is that the heatsink has a high spot where the screw is threaded into the sink. Knocking down the high spot and applying compound can make the transistor more reliable but it still runs very hot. It's far too hot to hold your finger on but generally cool enough for the transistor to survive. One of the tell-tale signs that a semiconductor has run hot for a long period of time is it's color. Many times, the black plastic turns brown. As you can see below, Q4901 has a brown tint compared to the other D600 transistor. You can also see that the leads have become discolored due to heat.
A slightly more complex solution is to insert a 'dropping' resistor in series with the transistor. Power dissipation is determined by the voltage across a device (the transistor) and the current flowing through that device. To reduce the power dissipation, you have to decrease at least one of the two. Inserting a dropping resistor reduces the voltage drop across the transistor (some is dropped across the resistor before transistor). When doing this, you have to be certain that the voltage isn't dropped to a point to where it affects the output of the transistor and doesn't exceed the power rating of the dropping resistor.
The following image is a wide-shot showing the transistor to the resistor that was added. More detailed photos will follow.
For this amp, a 47 ohm 7 watt resistor was used. It just happened to be what I had on hand but worked well. The following is a 100 ohm version of the same type of resistor (photo from 'resistors' page of this site).
The resistor was inserted into the circuit by desoldering the collector, soldering one resistor wire into the board and soldering the other resistor wire to the collector of the transistor.
When making modifications, you have to put a bit of thought into it to make it reliable and to prevent introducing new problems. The following photos will show what was done and why they were done. The first image shows the support for the wire at the transistor. This does several things. The most important is to take the stress off of the wire's solder connections. Some screws that hold the board are simply for support. Others have electrical connections to ground the heatsink. Sometimes they're critical and must be maintained. To maintain the connection below, the 18g magnet wire was stripped before it was bent to go around the screw. The wire was wrapped around the black/white wire and fixative was applied to prevent movement. This will prevent the wire from breaking and will make this easy to work with if the amp ever needs to be repaired again.
On the other end of the wire, a similar method was used. Here the wire didn't need to be stripped because there was no electrical connection. Fixative was again applied where the support wrapped around the wires.
To clamp the resistor to the heatsink, a clamp was bent and a 1/8" hole was drilled in it. You can see that heatsink compound was also applied but wasn't absolutely necessary since the resistor is dissipating significantly less than its rated power. It gets warm but not hot mounted like this.
A few notes for anyone working on this section of the amplifier...
The service manual voltages are wrong because they have the wrong pin configuration. The collector is at ground. The base is about 12v above the negative rail. The emitter is about 11.5v above the negative rail. You can place the black probe on the center leg of the negative rail rectifier adjacent to Q4901 to check the base and emitter voltages.
The Zener should have 12v (±10%) when the voltage is measured directly across it. The anode should be directly connected to the negative rail. The cathode is directly connected to the base of Q4901 (3rd leg).
The collector of Q4901 is directly connected to ground (primary and secondary grounds are tied together).
The emitter of Q4901 is directly connected to pin 3 of the IR2010S ICs.
You should read approximately 11.5v between pin 15 (black probe) and pin 3 (red probe) on the IR2010S ICs. The same voltage can be read across C9801 and C9802 or across the pads for E9801 and E9802 which are not installed.
When repairing class D amps, one of the questions you're likely to get is 'does the amp have rail-rail oscillation on the output transistors for the class D amp section'. It's sometimes difficult to explain what this is and posting photos for every time the question is asked is too time consuming. The following photos are for those who don't understand R-R oscillation. The first shows the scope with DC coupling (read the '' page of this site if you don't understand 'coupling'). This is the positive rail voltage. The negative rail voltage would be the same distance below the reference line as this is above the reference line.
When viewing the oscillation on the output transistors, you may not have the scope's timebase and/or trigger level set correctly and may see something like the waveform displayed in the following image. You can see that there is rail to rail activity but you cannot see the individual pulses.
The following image shows the waveform locked on the display. Note that the timebase is set to 2ms above (good starting point for audio, but not for the R-R carrier waveform) and is set to 5us in the image below. Again, these settings are discussed on the Oscilloscope page of the site.
This is a link to this site's home page.