• Short Circuit Protection System At The Amplifier Output System
• Short Circuit Protection System At The Amplifier Output Test
• Short Circuit Protection System At The Amplifier Output Definition

Basic Car Amplifier Repair Tutorial not to be confused with the(now available as a downloadable file)Foreword: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 fuse is ideal for protection against short circuits. Short circuits produce enough amperage to vaporize a fuse element and break connection in one cycle of a 60-cycle system. Fuses are more commonly used in devices connected to a system than within the system’s circuit. Testing UA741 op amp internal output short circuit protection for beginning learning electronics. //youtu.be/nyRpXa1IISw Negative 1 gain Inverting amplifier 741 op amp circuit build for.

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.Amp Going Into Protect Mode?If your amp is going into protect mode and you need to confirm that the amp is at fault, read through page. If you know that the amp is at fault and you want to try to repair it yourself, continue reading here.If You Need to Have an Amp RepairedThe information on this page is for those who are interested in trying to repair their own amplifiers. If you have no interest in repairing your own amp, you should look for a local repair shop before shipping the amp to be repaired.

For most amps, the round-trip for shipping alone will be approximately $60 if you use a shipper with real tracking. For large amps, the shipping can be well over $100. If you don't know any local repair shop or you don't know which repair shop is reliable, call all of the local car audio shops in the area and ask them who they'd recommend to have an amp repaired. If you find that most shops send their work to one particular repair shop, that shop likely does quality work.If You Need Internal PhotosIf you need internal photos of an amp to identify burned or missing components, me. If I have them I'll email them to you.Tips on Taking Photos when You Need Help with a RepairMany people ask for help with their amps when trying to do their own repairs.

Many times (most of the time) the photos are absolutely awful. It's generally not because their camera can't perform well enough.

It's generally due to a lack of effort to learn what the camera can or cannot do. Near the bottom of this page, there will be a section dedicated to helping you take better photos. Better photos will make it much easier for me to help you get your amp repaired. If you've already read the repair information on this page and only need to see the new tips on photographing amps, click.Tips for Email or Forum Posts when Asking for Repair AssistanceIf you're repairing an amplifier and need help, it's important that you do everything possible to make the transfer of information from you to me as efficient as possible. A few years ago, I had only a few people asking for help. Now I have to respond to hundreds of requests (literally) every week. To get to as many as people as possible, I need the information sent to me to be clear and concise.

A new section has been added to help you get the information I will need. If you've never read this page, continue reading below and you'll come to the section I've referred to here. If you've read this page repeatedly and want to go to the new section, click.

If you're too lazy or getting the amp repaired isn't important enough to CAREFULLY and COMPLETELY read this section, please don't email me for help. Too many people need help with repairs to help those who won't put forth the effort required to get their amp repaired.7mm Set Screws for Terminal BlocksIf you're looking for 7mm set screws for your amp's terminal blocks, click to go directly to the relevant section.NEW Alpine MRP-M1000This section was added because I get so many requests for help with these amps for one very specific problem. Click to go directly to the relevant section.Schematic Diagrams for Amplifiers:I will buy schematic diagrams. Do NOT send diagrams and expect me to pay for them without FIRST letting me know what you have and allowing me to tell you what I am willing to pay for them. I mainly need diagrams for Korean and Chinese made amplifiers.

If you have any that you want to sell, me and I'll let you know if I'm interested. There are some manufacturers that will provide schematics for free. I will pay for those also (if I don't yet have them) because I don't have time to collect all of them.Overview:This page is here to help answer many of the questions that I get about basic amplifier repair.

This is essentially a 'Cliffs-Notes' type page and isn't nearly as detailed as the I sell. However, it should answer many of the basic questions. Unless otherwise noted, this page will be dealing with class AB amplifiers (most full range amps are class AB or some variant, class A, class B). If you have a question about a repair, feel free to email me.Be Pro-active if you want to Learn to Repair Amplifiers:If you're interested in doing repair work and you have to constantly wait for someone to provide every minute detail, you probably won't make it in this business. For example, if someone states that the datasheet for an IRFZ44 provides specific information for that component and you ask the person helping you what a datasheet is, you are not well suited for this type of work. Someone well suited for this type of work would have immediately Googled 'datasheet' and 'IRFZ44' and would have immediately had the answer. This would save the time between the posts or emails from the person helping you with the repair (or whatever you're doing) and shows that you're thinking and willing to put forth a bit of effort.

This tells me a lot about a person's willingness/drive to learn. Too many people are lazy and would prefer to wait on an answer because that lets them relax and gives an excuse for doing nothing. If you're the type of person that prefers waiting, you are not likely well suited for any job where you have to think (and this type of work requires you to constantly use logic to find various faults). This may sound harsh and may make you angry (some people are very easily angered) but I know what it takes to make it in the repair business and being lazy won't cut it.Basic Amplifier Layout:Most amplifiers have switching power supplies. Generally, the power supply will be on the end of the amplifier near the B+ and ground terminals. The audio section of the amplifier is generally on the other end of the amplifier (most commonly the end where the RCA jacks are located). The power supply produces the various voltages required for the audio section.

If the power supply is blown, there will be no audio (in most cases).Very Important!The following is a list of things that will help you from making a few of the most common mistakes. In other words. If you don't want your amp to go up in flames, read the following very carefully (don't just skim over it). If the amplifier is under warranty and you break the warranty seals, the amp will not be covered by the manufacturer.

If it's under warranty, you should send it back to the manufacturer for repair. If you decide to repair the amplifier and you make mistakes, it could cost more than having the amp repaired by a repair shop. If you want to learn more about electronics, it may be worth the extra time and expense. If you simply want your amp to work properly and you have no interest in learning more about electronics, pay someone to repair your amplifier. When powering up an amplifier that you're repairing, you should do so with a 10 amp ATC/ATO fuse in the B+ power line.

A 15 amp ATC/ATO fuse may be required for amps rated over 1000 watts. If there is a serious problem causing excessive current draw, the fuse will help protect the amplifier. This is only used for low power and initial testing/troubleshooting. If you don't use a small fuse a very minor slip of a meter probe could result in hundreds of dollars worth of damage in a tiny fraction of a second. If the amp blows the fuse and you can't determine why (you can't find any defective parts and there is no direct short across the B+ and ground terminals), you need to power the amp up via a 2 ohm high-power resistor (25-100 watt resistor) or some other current limiter (some people use an automotive headlamp - an H6054 works relatively well). The resistor or headlamp will go in series with the B+ power supply wire. They limit the current going into the amplifier but generally allow enough current so that you can troubleshoot the problem.

Please note that the voltage at the amplifier will be significantly less than the supply voltage when the current limiter is inline and the amplifier has a fault that causes excessive current draw. Whenever possible, you should have the power semiconductors clamped tightly to the. It takes only seconds for a transistor to overheat and fail. Failure can occur even with the 10 amp fuse or current limiter in line.A note about PPI amplifiers.Some of the PPI amplifiers use the bottom cover to clamp the transistors to the heatsink. If you remove the bottom cover from one of these amplifiers, the transistors will not be clamped tightly to the heatsink and may fail within a few seconds if power is applied. The bottom cover must be securely fastened to the amp any time power is applied. If troubleshooting requires that the cover be removed, it may be necessary to to hold down the transistors so they don't overheat.

Any measurements made with the set to ohms or diode-check will be done with the amp disconnected from the power source. Voltage readings will be done with the amp powered up. Be sure not to allow the meter probes to slip and short between terminals of the components when measuring voltage. It's very important that you don't come into physical contact with any of the components inside the amp when it's powered up. After removing power from the amp, wait at least one minute before touching any components.

When measuring the voltage, the amplifier's main ground terminal is generally (but not always) a good reference point (for placement of the black meter probe). If you get strange voltage readings, me with the make and model number of the amp and I'll try to help you find the correct reference point.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.

Short Circuit Protection System At The Amplifier Output System

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.The download process and pricing structure for previous buyers has changed.The latest version (April, 2019) includes new content and features.Commonly Used TermsOn 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. Transistors:Transistors are used to control the flow of current. They are like valves.

There are many different types of transistors. In the power supply, you will almost exclusively find (Field Effect Transistors). In the audio section, the power transistors (those mounted to the heatsink that drive the signal to the speaker terminals) may be either FETs or.The power transistors in this amplifier are fully encapsulated. This is somewhat rare for the power transistors (fully encapsulated rectifiers are relatively common). If the amplifier has fully encapsulated transistors, you need to use the same type as replacements. The tab of the transistors here are completely insulated. In normal transistors, the metal tab is connected to the center terminal.

If the tab is allowed to contact the heatsink, it will cause the amp to fail. In amplifiers that don't use fully encapsulated components, you will see that they have between the transistor and the heatsink. Resistors:are used in every amplifier. They can be virtually any size.

Generally, larger resistors are used where higher power dissipation causes the resistor to run hot. In photo, you can see the large 'emitter resistors' and the smaller resistors. The small resistors are in a part of the circuit that causes very little power dissipation. The larger resistors are capable of dissipating more power and would fail (from overheating) if they were as small as the other resistors. All else being equal, larger resistors have more surface area which allows them to dissipate more heat than a smaller resistor. Transformers:The is used to step up the voltage from 12v to whatever is needed for the audio section of the amplifier. At 12v, the maximum power you can get is 20 watts into 4 ohms.

With higher voltage, you can produce more power. The main 'rail voltage' generated by power supplies in class AB car audio amplifiers is generally between ±30v and ±50v. In large class D amplifiers, the voltage can be greater than ±150v (I've measured more than 300v across the rails in some amps).In most amplifiers, the rail voltage can be measured on the center leg of the 3-legged, dual rectifiers.

In most class AB and class B amps (most full range amps fall into one of these categories) you will also find rail voltage on the center legs of the output transistors. Capacitors:are used to pass AC signals or to store energy. When used to pass AC signals (blocking DC), they are being used as coupling capacitors. When used to store energy, they are being used as filters. The large 'rail' capacitors are used to store energy. They provide energy between the pulses of the switching power supply.

In image, the rail capacitors are the ones on the left (blue). The capacitors on the right are the B+ filter capacitors. They are generally rated for higher operating temperatures. They also generally have lower ESR. This is important because high ripple current can cause capacitors with higher ESR to run hot and fail.

Gate Resistors:If you work on an amp that has a problem with the power supply, you're almost certainly going to see/hear the term 'gate resistor'. Here, the term indicates the way the resistor is being used in the circuit. The resistor passes the drive signal from the drive circuit (IC or transistors) to the gate leg of the power supply FET.

For most FETs, this is the left-most leg of the transistor. Click for the datasheet of a common FET.Understand What Your Multimeter is Telling YouWhen checking semiconductors, you will use a.

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:. Meter probes separated and not in contact with anything:This is an open circuit. If your meter's probes are across two points in a circuit and the meter reads the same as when the probes are not in contact with anything, the circuit is open (no connection). More accurately, this tells you that the circuit is open to DC current (the circuit is not capable of passing the DC current that the meter is applying to the circuit).

If you were using a meter that applied an AC voltage to the circuit (multimeters apply DC to the circuit), the reading may be different. Meters from various manufacturers will have various displays for an open circuit. 'OL' is very common. A Radio Shack meter of mine displays 'OF'. Another meter I have displays '1.

'. Meter probes touching:When you touch your meter's probes together, you should read all zeros (in diode test mode) or something very near 0 ohms (when set to ohms/resistance mode). If you don't have similar readings, you meter may be defective, it may have a low battery or the meter leads may be defective. Safety:Before you do any testing, you should set your meter to ohms and touch your probes together to make sure the meter is working properly and the leads are not defective. This is especially important when you're using your meter to confirm that there is no voltage in a circuit.

Of course, you must remember to set the meter to voltage mode before touching the probes to a circuit that could possibly have voltage on it. Some meters will be badly damaged if connected to a live circuit when they're set to ohms or diode check.Common SymptomsAmp Failure:There are many different ways that an amp can fail but the two most common failures are shorted and blown. The power supply FETs in this amp aren't blown. Many times (most of the time) power supply transistors are visibly damaged but that's not always true. If you clicked the links, you should have noticed that the power supply FETs were in a smaller case/package than the output transistors (look at the screw head for scale). In most instances for class A, class B or class, the output transistors have to dissipate more heat than the power supply transistors and the larger case makes it easier to transfer the heat from the transistor to the heatsink because there is more surface area on the large transistor case.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.Important:All of the transistors clamped to the heatsink are 'power transistors'. 'Power transistors' are typically any transistor capable of dissipating 10 or more watts of power. To dissipate the heat generated when dissipating that much power, they are typically clamped to a heatsink.

The FETs that drive the power transformers should be referred to as 'power supply transistors' or 'power supply FETs'. The transistors that are used to drive the rail voltage to the speakers should be referred to as 'output transistors'. If the transistors are FETs, you can refer to them as 'output FETs'.

When bipolar transistors are used as output transistors, they're typically referred to as simply 'output transistors', not 'output bipolars'.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 on the power supply transistors (near the ), 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:In general, when a transistor fails, it will either short (common for output AND power supply transistors) or open (common for power supply transistors). Transistors act like valves. They control the current flowing through a circuit. A shorted transistor acts like a valve that's stuck open (passing too much current). In the case of an output transistor, the shorted transistors tries to deliver the full rail voltage to the speaker output terminal. If you've ever seen a damaged amp that pushed or pulled the speaker cone to its limits when the amp powered up (common on some Rockford amplifiers), that was almost certainly due to a shorted output transistor. When checking transistors, you most commonly look for shorted connections inside the transistor.

You do this by using a multimeter to look for low resistance connections between the transistor's terminals.Note:I used the terms short and open on the previous paragraph. A short (short circuit) is a path through which current flows that should not be there. An open (open circuit) is a break in the circuit.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. 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. 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.Parallel ComponentsIn 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.DatasheetsDatasheets 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.These are FETs that you'll find in some amplifier's power supplies. They are rugged and relatively inexpensive.This part is packaged in several different ways. The different packages are used for various types of layouts (surface mount or through-hole).

The specifications are very similar except for the power dissipation rating. The larger components can dissipate more heat so they are rated higher.This is the most commonly used PWM control IC. It's used to drive the power supply transistors.

Most commonly, the IC drives a buffer circuit and the buffer drives the FETs. If you learn this IC, it will make it MUCH easier to troubleshoot amplifiers. After you've learned this IC, other driver ICs will be easier to learn. They all do the same basic thing but have slightly different features.Parts SubstitutionIn 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, 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 ComponentsSurface 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 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 page for more information on reading resistor values.Good Quality Equipment/ToolsAs with any type of work, it's easier to do a job with good quality tools. The following are some of my suggestions. Soldering Iron:When someone asks me to recommend a soldering iron, I always recommend Weller soldering irons. My favorite is the.

They can be purchased for $100. If that's more than you want to spend on an iron, the WP-35 is another good iron. If you've never used anything other than a budget/RS brand iron, you won't believe how much easier it is to make good solder joints with a professional quality iron.

Desoldering Pump:To replace defective components, you'll need to remove them from the board. To remove to old solder, I generally use a.

They are efficient and relatively inexpensive. I recommend the Edsyn DS017. I've tried others but none have been as reliable.

You can purchase these directly from. Desoldering Braid:Good quality is very good at cleaning up the pads for surface mount components. Don't buy the braid from Radio Shack. I've tried it several times and in every case, it was old and too oxidized to do any good. I generally buy Chem-Wik 10-100L. That's the 100ft roll. You'd likely buy the 10-5L or the 10-25L.

This braid has a rosin flux that helps draw the solder into the braid. You can purchase Chem-Wik braid from. Solder:I've used a lot of different brands of solder but now I almost exclusively use Kester 44. I've been using it for more than 10 years and the quality of the solder and the flux has always been top-notch. When you select a solder, you want rosin core solder, not acid core solder.

Acid core solder is for soldering copper pipes or radiators, not components on circuit boards. Multimeter:A good quality, reliable digital multimeter is an essential tool. The DMM is used check virtually all of the components in a piece of electronic equipment. As long as the meter is reliable and accurate, it doesn't need to have a lot of features.

Meter is just about as basic as you can get but it can perform virtually any test you need for basic repair work. I have lots of other meters (some much more expensive) but this is the meter I use on a daily basis (if you have a Fluke 10, 11 or 12 that you want to sell, email me). In addition to the basic volt/ohm functions, your meter should also have a diode-check function. If you're going to buy a meter, I strongly suggest buying a Fluke brand meter. Oscilloscopes:An oscilloscope isn't required to do all repairs but it allows you to confirm that the output is clean and that the power supply waveforms (particularly the gate drive waveforms) are as they should be.

You don't need a 200MHz scope for audio repair. I've used a (Tek 5110) and it worked perfectly well. If you want an inexpensive scope that will do virtually anything you'll never need for car audio amplifiers, you may want to try to find an old Tektronix 465 or.If you don't understand precisely what a scope does and how they function, read the page of this site (page #73).

There are a lot of people who have been using a scope for years and still don't know how to use them. For those people, there is a section labeled 'Best Initial Settings'.

That section tells you precisely how to set the scope for the most common tests performed in car audio amplifiers.At the of this page, I've posted a couple of photos and more information that may help you in your search for a usable scope. Power Supplies:When working on car audio amplifiers, it's not convenient to have to reinstall it in the vehicle for testing. You'll want to use an AC to DC converter (regulated 12v power supply).

These can vary in price. Surprisingly, Pyramid/Tenna supplies are pretty good. You'll need a supply rated to supply 35 amps continuously. If you can afford it get a larger one. I'd suggest buying a supply that has a meter to show current draw. Without the ammeter, you don't know if an amp is pulling excessive current.If you're on a tight budget, you can get by with a battery and battery charger but as soon as you can afford to buy something better, you should do so. It's not safe to charge a battery in a confined space and most chargers produce a lot of electrical noise/hum (not something you want when troubleshooting an amplifier).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.Back to Repair Information.Gate Drive Signal:I previously mentioned power supply drive circuits. Here, I'll go into a bit more detail.

The TL594 (or it's close relatives, the TL494 or the KA7500) produces the square wave drive signal. In some amplifiers, the power supply voltage is regulated. For regulated power supplies, the square wave output has a variable duty cycle. It modulates the pulse width to maintain the target rail voltage. This means the the 'on' time won't always be 100% (50% per output). For more information on PWM supplies, follow link.

For unregulated supplies, the pulse width is constant. For the, the output is typically taken from pins 9 and 10 (MTX, Sony and a few other amps use pins 8 and 11 as the outputs). This is driven into driver transistors. In photo, the drivers are the small rectangular components with the circuit board designations Q903, Q909, Q904 and Q910. They act as buffers and produce higher drive current than the TL595 can produce.The driver transistors drive the square wave signal into the (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 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:The output of the power transformer is sent to two. All of the positive pulses pass through one rectifier and to the positive rail capacitors.

The other other rectifier passes all of the negative pulses to the negative rail capacitor. This rail voltage is the source of power for the outputs transistors in the audio section of the amplifier.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:In most amplifiers, the rail voltage is much too high for the op-amps.

To lower the voltage, voltage regulators are used. There are many types of regulators. In this amplifier, Zener diodes are used to set the regulated voltage.

Series-pass transistors (BJTs) are used to increase the output current capacity of the regulator. The regulators for this amp can be seen.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:In most amplifiers, the input circuit is either an active noise cancelling circuit or the amplifier has an isolated secondary. You can find more information about these on page.

This amplifier uses an active noise cancelling circuit. Most budget amplifiers use an isolated secondary. The input op-amp is generally very near the RCA jacks like. It takes 2 op-amps for each input. Each of the 8 pin op-amp packages in the photo contains 2 op-amps.Crossovers/Filters:Not all op-amps are in flat packages. Dual op-amp is in an SIP (Single In-line Pin) package (vs the DIP, Dual In-line Pin package).

The op-amps in this package are being used in the filter (low pass crossover) circuit. The low pass/bypass switch on this amp selects between the crossover or the full range signal.Power Amplifier Section:After the switch, the signal is fed into the power amplifier section. In virtually all commercially available, solid state amplifiers, there is an error correction circuit. It greatly reduces the distortion at the output of the amplifier circuit.

The 'brains' of this error correction circuit is the 'differential amplifier'. The input signal is fed into the input of the differential amplifier. A fraction of the output circuit is fed back into the other side of the differential amplifier. If there is any difference in the two inputs of the differential amplifier, the error will be corrected.

In this amplifier, the two transistors of the differential amplifier are in. This insures that the transistors are closely matched and maintain the same temperature (which helps insure that they remain matched).Note:For most of the transistors using the Japanese numbering system, you add a 2S prefix to the part number. The dual transistor above is a 2SC5168. For transistors manufactured by KEC, the prefix is KT instead of 2S.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 and the driver transistors (2SC3421 and 2SA1358) drive the. 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 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. 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.Troubleshooting a Dead AmplifierPreviously, 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 (or whatever driver IC the amp uses). Using the, 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:. Make sure the IC has B+ voltage on its control and B+ inputs.

In general, the TL594 will have 12v on pins 8, 11 and 12. Without voltage on pin 12, the IC won't power up.

With no voltage on pins 8 and 11, it can't have output (most MTX, some Sony and some Xtant amps are different). All of the PWM control ICs have 5v regulators. Measure the voltage and make sure it's within a few percent of the rated voltage. On the TL594, pins 3 and 4 must be below 3v for the IC to produce output.

If it's above 4v, something is shutting the IC down. Pin 7 on the TL594 is ground. It must be directly connected to chassis ground. For an unregulated power supply, the on pins 9 and 10 will read 1/2 of the B+ voltage when using a multimeter set to DC volts. If the power supply transistors have failed, after you remove them, make sure that you read 1/2 B+ voltage all of the way to the gate of EACH power supply FET.

If it's too low or too high on any single FET or either bank of FETs, there is a problem. If it's a problem on a single FET, the gate resistors is likely open for that FET. If the problem is the same for a bank of FETs, the problem is in the IC or in the buffer/driver circuit. Pin 5 should have 1.5v DC on it. This is actually a but it typically reads 1.5v on a multimeter. Previously, I stated that the voltage on pins 3 and 4 had to be below 3v.

Pin 3 has to be below the peak voltage of this waveform. Pin 4 must be 0.15v below the peak voltage. Pins 1, 2, 15, and 16 are the error amps and drive pin 3 internally (see datasheet for internal schematic).

The error amps are used for various purposes. It's common for pins 1 and 2 to be used for voltage regulation. Pins 15 and 16 are often unused. When unused, pin 15 is tied to 5v (pin 14) and pin 16 is tied to ground. These are comparators and you can read about those (demo 1/2 of the way down the page).Protection CircuitsProtection 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.The most common protection circuit is the thermal shutdown circuit.

Short Circuit Protection System At The Amplifier Output Test

It is designed to shut the amp down if it gets too hot.Most amplifiers also have an over-current protection circuit. It's designed to shut the amp down if too much current is drawn from the speaker outputs or when there is an internal fault that causes excessive current draw.Some amplifiers have DC offset protection. This prevents damage to the speakers in case the amp fails in a way that causes rail voltage to be driven to the speaker output terminals.Over and under-voltage protection is employed in some amplifiers. If the B+ supply voltage is too high or too low, the amp will shut down.Any of these can shut the amp down.

Short Circuit Protection System At The Amplifier Output Definition

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.