AMPLIFIER REPAIR

Troubleshooting is usually carried out in the following sequence:Determination of a faulty cascade in the device. Troubleshooting a part in a cascade. Analysis of the causes of component failure. Selection and replacement of parts.Post-repair check and adjustment of cascades in the device.

When the audio amplifier is not working, you can touch the output chips or transistors with your finger. If they are cold at normal supply voltage and input signal, then no current passes, which in normal mode should warm them up. If the transistors are very hot, this also indicates a malfunction. The stabilizer is checked in the same way. Warm electrolytic capacitors of large filter capacity or with signs of breakdown also need to be replaced.
During an external inspection, you can lightly tap the board with the handle of a screwdriver. If contact is lost, crackling and rustling noises will appear when you touch the device.To find a fault, measure the operating modes of transistors or microcircuits using direct and alternating current.

We determine a defect in the power supply starting with checking the serviceability of the power cord and fuses. If the fuses are intact and the mains voltage reaches the primary winding of the transformer, but there is no voltage at the output, the fuse may be built into the transformer. This fuse is present in most transformers and is mounted on top of the primary winding. If this fuse is not present, and there is a break in the primary winding, the transformer will have to be replaced. You should find out what the secondary voltages should be and select a ready-made transformer, or even install two if a transformer with all the required voltages could not be found. You can find out the value of the voltages in the secondary winding circuits if you determine the nameplate supply voltage using one of the output microcircuits. Voltage inscriptions on the power filter capacitors will also help. As a rule, they are placed with a 30% margin.

Failure of an audio power amplifier often occurs due to a short circuit of the amplifier output to a common wire or housing. In most equipment, power amplifiers are made on microcircuits, and repair consists of simply replacing the microcircuit. But there are times when it is difficult to find a similar microcircuit, and it is not possible to select an analogue. If the ULF circuit could not be found, you can repair the device by using, instead of a burnt microcircuit, a standard ULF on TDA 1552 - TDA 1558. These microcircuits do not require almost any attachments for operation and replacing any integrated power amplifier with one of these microcircuits will be very simple.

Repair method for UMZCH

UMZCH repair is almost the most common question asked on amateur radio forums. And at the same time – one of the most difficult.

Of course, there are “favorite” faults, but in principle, any of several dozen, or even hundreds of components that make up the amplifier can fail. Moreover, there are a great many UMZCH circuits. Of course, it is not possible to cover all cases encountered in repair practice, however, if you follow a certain algorithm, then in the vast majority of cases it is possible to restore the device’s functionality in a very reasonable time. This algorithm was developed by me based on my experience in repairing about fifty different UMZCHs, from the simplest, for a few watts or tens of watts, to concert “monsters” of 1...2 kW per channel, most of which came in for repair.

without circuit diagrams

1. The main task of repairing any UMZCH is to localize the failed element, which entails the inoperability of both the entire circuit and the failure of other cascades. Since in electrical engineering there are only 2 types of defects:
2. presence of contact where there should not be;

lack of contact where it should be,

then the “ultimate task” of repair is to find a broken or torn element. And to do this, find the cascade where it is located. Next is “a matter of technology.” As doctors say: “The correct diagnosis is half the treatment.”

1. List of equipment and tools necessary (or at least highly desirable) for repairs:
2. Screwdrivers, side cutters, pliers, scalpel (knife), tweezers, magnifying glass - i.e., the minimum required set of ordinary installation tools.
3. Tester (multimeter).
4. Oscilloscope.
5. Low frequency sinusoidal voltage generator (highly desirable).
6. Bipolar regulated power supply 15...25(35) V with output current limitation (highly desirable).
7. Capacitance and equivalent series resistance meter ( ESR ) capacitors (highly desirable).
8. And finally, the most important tool is a head on your shoulders (required!).

Let's consider this algorithm using the example of repairing a hypothetical transistor UMZCH with bipolar transistors in the output stages (Fig. 1), which is not too primitive, but not very complicated either. This scheme is the most common “classic of the genre”. Functionally, it consists of the following blocks and nodes:

A) bipolar power supply (not shown);

b) transistor differential input stage VT 2, VT 5 with transistor current mirror VT 1 and VT 4 in their collector loads and a stabilizer of their emitter current at VT 3;

V) voltage amplifier VT 6 and VT 8 in cascode connection, with a load in the form of a current generator on VT 7;

G) quiescent current thermal stabilization unit on a transistor VT 9;

e) unit for protecting output transistors from overcurrent on transistors VT 10 and VT 11;

e) current amplifier on complementary triplets of transistors connected according to a Darlington circuit in each arm ( VT 12 VT 14 VT 16 and VT 13 VT 15 VT 17).

Rice. 1.

1. The first point of any repair is an external inspection of the subject and sniffing it (!). This alone sometimes allows us to at least guess the essence of the defect. If it smells burnt, it means something was clearly burning.

1. Checking the presence of mains voltage at the input: the mains fuse has blown, the fastening of the power cord wires in the plug has become loose, there is a break in the power cord, etc. The stage is the most banal in its essence, but at which the repair ends in approximately 10% of cases.

1. We are looking for a circuit for the amplifier. In the instructions, on the Internet, from acquaintances, friends, etc. Unfortunately, more and more often lately it has been unsuccessful. If we didn’t find it, we sighed heavily, sprinkled ashes on our heads and started drawing a diagram on the board. You can skip this step. If the result doesn't matter. But it's better not to miss it. It’s boring, long, disgusting, but - “It’s necessary, Fedya, it’s necessary...” ((C) “Operation “Y”...).

1. We open the subject and carry out an external inspection of its “gibles”. Use a magnifying glass if necessary. You can see destroyed housings of semi-automatic devices, darkened, charred or destroyed resistors, swollen electrolytic capacitors or electrolyte leaks from them, broken conductors, printed circuit board tracks, etc. If one is found, this is not yet a reason for joy: destroyed parts may be the result of the failure of some “flea” that is visually intact.

1. Checking the power supply. Unsolder the wires coming from the power supply to the circuit (or disconnect the connector, if any). We take out the mains fuse and solder a 220 V (60…100 W) lamp to the contacts of its holder. It will limit the current in the primary winding of the transformer, as well as the currents in the secondary windings.

Turn on the amplifier. The lamp should blink (while the filter capacitors are charging) and go out (a faint glow of the filament is allowed). This means that K.Z. There is no mains transformer on the primary winding, and there is no obvious short circuit. in its secondary windings. Using a tester in alternating voltage mode, we measure the voltage on the primary winding of the transformer and on the lamp. Their sum must be equal to the network one. We measure the voltage on the secondary windings. They must be proportional to what is actually measured on the primary winding (relative to the nominal). You can turn off the lamp, replace the fuse and plug the amplifier directly into the network. We repeat the voltage check on the primary and secondary windings.

The relationship (proportion) between them should be the same as when measuring with a lamp.

The lamp is constantly burning at full intensity - this means we have a short circuit. in the primary circuit: we check the integrity of the insulation of the wires coming from the network connector, the power switch, the fuse holder. We unsolder one of the leads going to the primary winding of the transformer. The lamp goes out - most likely the primary winding (or interturn short circuit) has failed.

1. It was determined that the transformer is in order, and the defect is in the rectifiers or filter capacitors. We test the diodes (it is advisable to unsolder them under one wire going to their terminals, or unsolder them if it is an integral bridge) with a tester in ohmmeter mode at the minimum limit. ESR Digital testers often lie in this mode, so it is advisable to use a pointer device. Personally, I have been using a beeper for a long time (Fig. 2, 3). Diodes (bridge) are broken or broken - we replace them. Whole – “ring” filter capacitors. Before measurement, they must be discharged (!!!) through a 2-watt resistor with a resistance of about 100 Ohms.

Otherwise, you may burn the tester. If the capacitor is intact, when it closes, the needle first deflects to the maximum, and then quite slowly (as the capacitor charges) “creeps” to the left. We change the connection of the probes. The arrow first goes off scale to the right (there is a charge left on the capacitor from the previous measurement) and then creeps to the left again. If you have a capacitance meter and

1. , then it is highly advisable to use it. We replace broken or broken capacitors.

1. Rice. 2. Fig. 3.

The lamps do not light up or only one of them lights up. This means that the output stages are most likely intact. We connect a 10…20 Ohm resistor to the output. Turn it on. The lamps should blink (there are usually also power supply capacitors on the board). We apply a signal from the generator to the input (the gain control is set to maximum). The lamps (both!) lit up. This means that the amplifier amplifies something (although it wheezes, vibrates, etc.) and further repair consists of finding an element that takes it out of mode. More on this below.

1. For further testing, I personally do not use the amplifier’s standard power supply, but use a 2-polar stabilized power supply with a current limit of 0.5 A. If there is none, you can also use the amplifier’s power supply, connected, as indicated, through incandescent lamps. You just need to carefully insulate their bases so as not to accidentally cause a short circuit and be careful not to break the flasks. But an external power supply is better. At the same time, the current consumption is also visible. A well-designed UMZCH allows supply voltage fluctuations within fairly wide limits. We don’t need its super-duper parameters when repairing, just its performance is enough.

1. So, everything is fine with the BP. Let's move on to the amplifier board (Fig. 4). First of all, you need to localize the cascade(s) with broken/broken component(s). For this extremely preferably have an oscilloscope. Without it, the effectiveness of repairs drops significantly. Although you can also do a lot of things with a tester. Almost all measurements are made without load(at idle). Let us assume that at the output we have a “skew” of the output voltage from several volts to the full supply voltage.

1. First, we turn off the protection unit, for which we unsolder the right terminals of the diodes from the board VD 6 and VD 7 (in my practice it was three case when the cause of inoperability was the failure of this particular unit). We look at the voltage output. If it returns to normal (there may be a residual imbalance of several millivolts - this is normal), call VD 6, VD 7 and VT 10, VT 11. There may be breaks and breakdowns of passive elements. We found a broken element - we replace and restore the connection of the diodes. Is the output zero? Is the output signal (when a signal from the generator is applied to the input) present? The renovation is complete.

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Rice. 4.

Has anything changed with the output signal? We leave the diodes disconnected and move on.

1. We unsolder the right terminal of the OOS resistor from the board ( R 12 together with the right output C 6), as well as left conclusions R 23 and R 24, which we connect with a wire jumper (shown in red in Fig. 4) and through an additional resistor (without numbering, about 10 kOhm) we connect to the common wire. We bridge the collectors with a wire jumper (red color) VT 8 and VT 7, excluding capacitor C8 and the thermal stabilization unit for the quiescent current. As a result, the amplifier is separated into two independent units (input stage with a voltage amplifier and output follower stage), which must work independently.

Let's see what we get at the output. Is the voltage imbalance still there? This means that the transistor(s) of the “skewed” shoulder are broken. We unsolder, call, replace. At the same time, we also check passive components (resistors). The most common variant of the defect, however, I must note that very often it is consequence

failure of some element in the previous cascades (including the protection unit!). Therefore, it is still advisable to complete the following points. R 23 and R Is there any skew? This means that the output stage is presumably intact. Just in case, we apply a signal from the generator with an amplitude of 3...5 V to point “B” (resistor connections

24). The output should be a sinusoid with a well-defined “step”, the upper and lower half-waves of which are symmetrical. If they are not symmetrical, it means that one of the transistors of the arm where it is lower has “burned out” (lost parameters). We solder, we call. At the same time, we also check passive components (resistors).

Is there no output signal at all?

1. This means that the power transistors of both arms flew out “through and through”. It's sad, but you'll have to unsolder everything and ring and then replace it. Breakage of components is also possible. Here you really need to turn on the “8th instrument”. We check, replace... Have you achieved symmetrical repetition at the output (with a step) of the input signal? The output stage has been repaired. Now you need to check the functionality of the quiescent current thermal stabilization unit (transistor R VT 9). Sometimes there is a violation of the contact of the variable resistor motor 22 with resistive track.

However (very often), a tuning resistor is placed between the collector and the VT9 base. An extremely foolproof option! Then, if the motor loses contact with the resistive track, the voltage at the base of VT9 decreases, it closes and, accordingly, the voltage drop between its collector and emitter increases, which leads to a sharp increase in the quiescent current of the output transistors, their overheating and, naturally, thermal breakdown. An even more stupid option for performing this cascade is if the VT9 base is connected only to the variable resistor motor. Then, if contact is lost, anything can happen on it, with corresponding consequences for the output stages.

If possible, it is worth rearranging R 22 into the base-emitter circuit. True, in this case the adjustment of the quiescent current will become distinctly nonlinear depending on the angle of rotation of the engine, but IMHO This is not such a big price to pay for reliability. You can simply replace the transistor Breakage of components is also possible. Here you really need to turn on the “8th instrument”. We check, replace... 9 to another, with the opposite type of conductivity, if the layout of the tracks on the board allows. This will not affect the operation of the thermal stabilization unit in any way, because he is two-terminal network and does not depend on the conductivity type of the transistor.

Testing this cascade is complicated by the fact that, as a rule, connections to the collectors VT 8 and VT 7 are made by printed conductors. You will have to lift the legs of the resistors and make connections with wires (Figure 4 shows wire breaks). Between the positive and negative supply voltage buses and, accordingly, the collector and emitter Breakage of components is also possible. Here you really need to turn on the “8th instrument”. We check, replace... 9, resistors of approximately 10 kOhm are turned on (without numbering, shown in red) and the voltage drop across the transistor is measured Breakage of components is also possible. Here you really need to turn on the “8th instrument”. We check, replace... 9 when rotating the trimmer resistor engine R 22. Depending on the number of repeater stages, it should vary within approximately 3...5 V (for “triples, as in the diagram) or 2.5... 3.5 V (for “twos”).

1. So we got to the most interesting, but also the most difficult - the differential cascade with a voltage amplifier. They only work together and it is fundamentally impossible to separate them into separate nodes.

We bridge the right terminal of the OOS resistor R 12 with VT 8 and VT manifolds 7 (dot " A", which is now his "exit"). We get a “stripped-down” (without output stages) low-power op-amp, which is fully operational at idle (without load). We apply a signal with an amplitude from 0.01 to 1 V to the input and see what happens at the point A. If we observe an amplified signal with a shape symmetrical relative to the ground, without distortion, then this cascade is intact.

1. The signal is sharply reduced in amplitude (low gain) - first of all, check the capacitance of the capacitor(s) C3 (C4, since, to save money, manufacturers very often install only one polar capacitor for a voltage of 50 V or more, expecting that in reverse polarity it will still work, which is not gut). When it dries out or breaks down, the gain decreases sharply. If there is no capacitance meter, we simply check by replacing it with a known good one.

The signal is skewed - first of all, check the capacitance of capacitors C5 and C9, which shunt the power buses of the preamplifier section after resistors R17 and R19 (if these RC filters exist at all, since they are often not installed).

The diagram shows two common options for balancing the zero level: with a resistor R 6 or R 7 (there may, of course, be others), if the contact of the motor is broken, the output voltage may also be skewed. Check by rotating the engine (although if the contact is “completely broken”, this may not give a result). Then try to bridge their outer terminals with the output of the engine using tweezers.

There is no signal at all - we look to see if it is even present at the input (break in R3 or C1, short circuit in R1, R2, C2, etc.). Just first you need to unsolder the VT2 base, because... the signal on it will be very small and look at the right terminal of resistor R3. Of course, the input circuits may differ greatly from those shown in the figure - include the “8th instrument”. Helps.

1. Naturally, it is not realistic to describe all possible cause-and-effect variants of defects. Therefore, further I will simply outline how to check the nodes and components of this cascade.

Current stabilizers VT 3 and VT 7. Breakdowns or breaks are possible in them. The collectors are desoldered from the board and the current between them and the ground is measured. Naturally, you first need to calculate based on the voltage at their bases and the values ​​of the emitter resistors, what it should be. ( N. B .! In my practice, there was a case of self-excitation of an amplifier due to an excessively large resistor value R 10 supplied by the manufacturer.

It helped to adjust its nominal value on a fully working amplifier - without the above-mentioned division into stages). Breakage of components is also possible. Here you really need to turn on the “8th instrument”. We check, replace... You can check the transistor in the same way. Breakage of components is also possible. Here you really need to turn on the “8th instrument”. We check, replace... 8: if you jumper the collector-emitter of the transistor

6, it also stupidly turns into a current generator. Transistors of the differential stage VT 2 V 5 T and current mirror 6 are checked by checking them after desoldering. It is better to measure the gain (if the tester has such a function). It is advisable to choose ones with the same gain factors.

1. A few words “off the record.” For some reason, in the overwhelming majority of cases, transistors of greater and greater power are installed in each subsequent stage. There is one exception to this dependence: on the transistors of the voltage amplification stage ( VT 8 and VT 7) dissipates 3…4 times more power than on pre-driver ones VT 12 and VT 23 (!!!). Therefore, if possible, they should be immediately replaced with medium power transistors. A good option would be KT940/KT9115 or similar imported ones.

1. Quite common defects in my practice were non-soldering (“cold” soldering to tracks/“spots” or poor servicing of the leads before soldering) of component legs and broken leads of transistors (especially in a plastic case) directly near the body, which were very difficult to see visually. Shake the transistors, carefully observing their terminals. As a last resort, unsolder and solder again.

If you have checked all the active components, but the defect remains, you need (again, with a heavy sigh), remove at least one leg from the board and check the ratings of the passive components with a tester. There are frequent cases of breaks in permanent resistors without any external manifestations. Non-electrolytic capacitors, as a rule, do not break through/break, but anything can happen...

1. Again, based on repair experience: if darkened/charred resistors are visible on the board, and symmetrically in both arms, it is worth recalculating the power allocated on it. In the Zhytomyr amplifier " Dominator “The manufacturer installed 0.25 W resistors in one of the cascades, which regularly burned (there were 3 repairs before me). When I calculated their required power, I almost fell out of my chair: it turned out that they should dissipate 3 (three!) watts...

1. Finally, everything worked... We restore all the “broken” connections. The advice seems to be the most banal, but how many times is it forgotten!!! We restore in the reverse order and after each connection we check the amplifier for functionality. Often, a step-by-step check seemed to show that everything was working properly, but after the connections were restored, the defect “crept out” again. Lastly, we solder the diodes of the current protection cascade.

1. We set the quiescent current. Between the power supply and the amplifier board we turn on (if they were turned off earlier) a “garland” of incandescent lamps at the corresponding total voltage. We connect an equivalent load (4 or 8 ohm resistor) to the UMZCH output. Trimmer motor R 22 is set to the lower position according to the diagram and the input is supplied with a signal from a generator with a frequency of 10...20 kHz (!!!) of such an amplitude that the output howls a signal of no more than 0.5...1 V. At such a level and frequency of the signal, “ step”, which is difficult to notice at a large signal and low frequency. By rotating the R22 engine we achieve its elimination. In this case, the filaments of the lamps should glow a little. You can also monitor the current with an ammeter by connecting it in parallel with each garland of lamps. Don’t be surprised if it differs noticeably (but no more than 1.5…2 times more) from what is indicated in the setup recommendations - after all, what’s important to us is not “following the recommendations,” but the sound quality! As a rule, in “recommendations” the quiescent current is significantly overestimated to ensure that the planned parameters are achieved (“at worst”). We bridge the “garlands” with a jumper, increase the output signal level to a level of 0.7 from the maximum (when the amplitude limitation of the output signal begins) and let the amplifier warm up for 20...30 minutes. This mode is the most difficult for the transistors of the output stage - the maximum power is dissipated on them. If the “step” does not appear (at a low signal level), and the quiescent current has increased no more than 2 times, we consider the setup complete, otherwise we remove the “step” again (as indicated above).

1. We remove all temporary connections (don’t forget!!!), assemble the amplifier completely, close the case and pour a glass, which we drink with a feeling of deep satisfaction for the work done. Otherwise it won't work!

Of course, this article does not describe the nuances of repairing amplifiers with “exotic” stages, with an op-amp at the input, with output transistors connected with an OE, with “double-deck” output stages, and much more...

Falconist

It's no secret that to get high-quality sound and powerful bass in a car, you definitely need a power amplifier. Today, fortunately, you can find car amplifiers on the market to suit every taste, it all depends on your specific needs. To power standard car speakers, an amplifier of 200-400 watts is enough, but among us there are true connoisseurs of sound pressure, audiophiles and music lovers, who will not be surprised by a couple of hundred watts of sound power.

It is for such people that class D amplifiers were invented - digital audio amplifiers that have high efficiency, compact size and many other advantages.

Unfortunately, a car amplifier sometimes breaks down, in some cases the repair is more expensive than the initial cost of the amplifier itself, so it is very advisable to consider or try to repair it yourself, because sometimes the cause of the breakdown can be a blown fuse. Having at hand a simple and cheap multimeter with a diode testing mode, you can find most of the defects that are very often observed in many car amplifiers.

Any car amplifier consists of three main parts - a voltage converter, a block with power amplifiers and a filter block (crossover).

The voltage converter or inverter is the most vulnerable part in any amplifier - 90% of problems are related to this unit. The converter essentially powers the entire amplifier, including the filter bank.

Exclusively all voltage converters are made according to a standard push-pull circuit using a PWM controller, most often on TL494. Then everything is standard - driver, power transistors, transformer, rectifier and filter unit. Some amplifiers (cheap) implement inverter circuits of an unstabilized type - in a word, there is no control of the output voltage, of course this is quite bad, but it is not a necessary process at all if the amplifier is not sensitive to the supply voltage and is a cheap model.

Converter transistors are the ones that fail most often. In cheap Chinese amplifiers, the transistors are strangely marked, even if you can’t find similar transistors, then you just need to know one thing - the keys can always be replaced with IRFZ40/IRFZ44/IRFZ46/IRFZ48 or with the more powerful IRF3205, the choice of keys is actually quite large, I just listed the most available options. In general, exclusively in all car inverters, high-power N-channel field-effect transistors are used - up to the brutal IRF1404.

Initially, we check the board by eye - sometimes visible defects may be observed (burnt out resistor, broken tracks on the back side of the board, etc.)

Before replacing transistors, you must first check the power fuse, the diode on the plus and minus buses (when the power is reversed, it also burns out), and only after you are convinced that everything is ok with these parts, we replace the keys.

For more professional repairs, you can’t do without an oscilloscope. Initially, you need to check for the presence of rectangular pulses on the 9th and 10th pins of the generator microcircuit; if they are present, then the microcircuit is working. Next, we check for the presence of the same pulses after the driver - on the gates of the field switches. If there are no pulses, then most likely the problem is in the driver; if there are, then without hesitation we replace the field-effect transistors.

It is extremely rare that there is a problem with the power amplifier; the converter burns out first, saving the amplifiers. Other breakdowns are possible in the converter, although they are very rare. There may be a problem with the input and output capacitors or the diode rectifier, which rectifies high-frequency alternating voltage from the transformer.

After all, as they say in the narrow circles of radio mechanics - “In electronics there are only two types of faults”:

1. Presence of contact where there should not be.
2. Lack of contact where it should be.

List of technical equipment required for repairs:

1. Screwdrivers of various designs, side cutters, pliers, a mounting knife, tweezers, a magnifying glass - that is, what is needed at a minimum for repairs.
2. The measuring device is multimeters.
3. An adjustable bipolar power supply for 16...24 or 36v, preferably with an output current limiting function.
4. And lastly, experience in electronics repair.

Determining the malfunction should begin by checking the output voltage - whether it is there or not. If it is missing, the fuse may simply have blown, there is no reliable contact at the wire terminal, etc. The moment is standard and ordinary, but it is at this stage that in 10% of cases the repair is completed.

The next steps when you start should be: - search for a circuit diagram for the amplifier; if you can’t find it, then you’ll have to rely on your experience and knowledge. We remove the cover of the device and begin a visual inspection of the printed circuit board to identify leaks or swelling of electrolytic capacitors, blackening of resistors, broken printed tracks, etc. Sometimes only such an inspection makes it possible to quickly identify a part that has failed. Then, with the amplifier turned on, you need to check all the components installed on the board with a touch of your finger. If strong heat is generated on the element, then we can assume that the problem may be there.

Car audio amplifier repair- this is troubleshooting not only in the sound amplification path, but also in the main unit of the amplifier - the power source. We examine the power supply and output voltage. Basically, automobile ULFs have bipolar ones from 20v and more. If we find blackened resistors or broken transistors, we replace them with serviceable ones.

The actual sequence of checking actions is as follows:

We turn on the amplifier, after applying voltage, you need to short-circuit the Remout input to the “+” power supply (or to “-” in different ways everywhere) and observe the Protect protection indicator, if the LED lights up, therefore, the amplifier has switched to protection mode. This can happen due to a malfunction of the voltage conversion module or a broken transistor junction in one of the arms. Also, the cause of the breakdown may be a lack of power to the microcircuit installed in the transistor circuit of the converter (usually TL494 or others are installed there).

In addition, the protection of a car power amplifier can also be triggered if one or several UMZCH transistors of one of the channels are knocked out. When the transistor of the output stage of the PA is knocked out, a short circuit occurs, creating a colossal load in the PN circuit. As a result, the protection is immediately activated.

Therefore, continuing car audio amplifier repair, and after turning on the power to the amplifier the fuse remains intact, then you need to check the output voltage on the converter, which should be 2 x 20v or more (bipolar). Most likely, when the protection indicator is lit, there will be no voltage in the output voltage circuit. Based on this, it is necessary to disconnect the PA from the converter. One of the most convenient options may be to unsolder the transistor leads one at a time on each channel or unplug them all. After the terminals of the MOSFET transistors are unsoldered and the amplifier turns on normally, the protection LED does not light up. Then we use the method of ringing transitions to find the broken field field and change it.

If the LED continues to light when voltage is applied, then we continue to look for a fault in the converter. First of all, we determine whether there is voltage on the PN microcircuit; transistors in the voltage supply path to the microcircuit may burn out. Pay special attention to the transformer, see if there are any singed turns of the enamel wire or a break. It would also be a good idea to sniff to see if there is a burning smell. In some models of car amplifiers, diode assemblies are installed in the converter circuit between the amplifier, which can also cause the protection to trip.