The complexity of repairing sound amplifiers depends entirely on the type of faulty part and its location in the power amplifier blocks.
What will be needed for diagnosis and repair:
- User's manual
- Soldering iron
- Turn off the amplifier and set the volume to zero.
- Turn on the amplifier. If the LED indicator indicating the “on” position is lit, then you can eliminate a malfunction in the power supply. In normal operating mode, smoothly increase the sound volume. If there is sound coming from the speakers, but it is distorted or sounds too quiet, this means that the power amplifier is functioning, but not in optimal mode. Check cable connection. If there is no sound from the speakers, the amplifier unit is malfunctioning.
- Unscrew the rear panel and extend the chassis. Unscrew the top case cover to view the boards. Check for visible signs of damage to components such as fuses or transistors. They will be brown in places of burnout. If you notice blown fuses or transistors, you should try to replace them with identical parts.
- Check wires and solder joints. If it was possible to detect a defect in soldering, use a soldering iron and reconnect. Brush off any traces of soldering.
- Next, we study the board for faulty capacitors or resistors. In the event of a malfunction, any of these parts closes the circuit.
- Check with a multimeter resistor. Each resistor has its own rating, marked on the board. When you turn on the power of the amplifier and measure the resistance of the resistor, a deviation of 5 percent from the nominal value is allowed. If the deviation of the indicators is more than 5 percent, the resistor is faulty. If the indicator is zero, the resistor is fully closed.
- Turn off the amplifier and replace the resistor.
- Check transformer outputs. When the amplifier is on, measure the readings on the primary winding of the transformer. Zero readings indicate a short circuit in the coil; high readings indicate a leak. In both cases, replacement is required.
If, for any reason, independent troubleshooting is difficult, contact our service center.
Real examples of repair amplifiers for cars
Here I will share my modest experience in the field of repair of car amplifiers. I hope the information is useful to beginner radio mechanics in their difficult task of restoring audio equipment, as well as car enthusiasts who are familiar with electronics and who want to fix their amplifier themselves.
To begin with, I would like to talk about how to turn on the car amplifier without a car radio and at home. Read more about this here. This will be needed when repairing an auto amplifier.
If you don’t have a sufficiently powerful power supply at hand, then any one suitable for 12V voltage and a current of 1-3 amperes is suitable. But here it is worthwhile to understand that we need it only to turn on and set up the amplifier. We will not use it at full power, so the current consumption will be minimal.
I also highly recommend reading or taking note of the material on the device of the converter of the car amplifier. This information is very important.
Well, now, repair examples from real practice. Basically, they relate to one of the main blocks of any car amplifier - a voltage converter, or in another way - an inverter.
Repair of car amplifiers CALCELL.
1. Fault: the car goes into defense. The red PRT LED (Protect - “protection”) is lit on the front panel. After a couple of starts, the amplifier stopped showing signs of life at all - the PRT LED turned off.
The cause of the malfunction turned out to be the 2N4403 transistor in the circuit of the TL494CN chip (converter). One of his crossings was broken. In addition, a 10Ω (Ohm) resistor burned out. In the photo, R7 is him. While the resistor "tolerated" - the amplifier turned on, but went into defense. As it burned out, the amplifier stopped turning on at all.
The pinout of the bipolar P-N-P transistor 2N4403.
Why did the amplifier go into defense? The fact is that this transistor is part of the on / off circuit. Due to the breakdown of the P-N junction of the transistor, the amplifier did not turn on and went into protection.
At hand, there was no suitable PNP replacement for the 2N4403 transistor. Therefore, a risky attempt was made to take the same transistor from the preliminary stage of one of the amplifier channels. Fortunately, they were there. Yes, you think, I decided, well, I’ll get the transistor out of there, solder it instead of the faulty one, check the amplifier. Ay, yes, I did. But after a few seconds after turning on, I smelled a burning smell. It turned out that due to the lack of 1 small transistor, the powerful complementary transistors of the output stage of the UMZCH began to warm terribly. Fortunately, the transistors survived. Therefore, I do not advise so "trick".
Replacing the transistor was complicated by the fact that it was smeared with some kind of rubber glue that glued barrels of electrolytes to the circuit board.
2. Amplifier CALCELL POP 80.4 does not turn on. Protective fuses blow.
The device came "dead", apparently after an incorrect connection. After a quick inspection of the parts without soldering, it turned out that a 11V zener diode was broken in the "strapping" of the TL494CN PWM controller chip. A breakdown of the TL494CN chip itself was also detected. When measuring the resistance between terminal 12 (+ power, Vcc) and 7 (- power, GND) The multimeter showed - "0". Apparently, the power supply voltage of the amplifier was greatly overestimated.
After replacing the TL494CN chip and the 11V zener diode, an attempt was made to turn on the amplifier. But, after switching on, the red PRT LED lights up for a few seconds (as it should be), and then complete silence. . The power supply from which the amplifier was powered went into protection due to overcurrent.
It turned out that one of the two groups of MOSFETs on the converter board is very hot. The transistors of the other group are cold. After checking the 3 STP75NF75 transistors that were warming up, it turned out that they were broken (Source - Stoke). The 2N4403 transistor, which is a buffer for this converter arm, was also punched. For more details on the scheme of a typical converter (inverter) of an auto amplifier, see here.
After replacing the 2N4403 buffer transistor and three STP75NF75 MOSFETs (labeled P75NF75), the auto amplifier began to work properly.
3. Amplifier CALCELL POP 80.4.When the amplifier is turned on, the red LED lights up "PROTECT" and after a few seconds it goes dead. The amplifier does not turn on - there is no indication.
This happens when the converter goes into protection due to high current consumption or short circuit in the load. The load in this case is all four amplifiers, a filter unit and preamps.
The most likely reason for the protection to trip is the failure of the output transistors. The CALCELL POP 80.4 amplifier uses powerful bipolar transistors as the output transistors. You can evaluate their serviceability using this technique, and it is not necessary to solder the transistors. As a rule, the breakdown of the transition of the transistor is easily determined, the multimeter starts to squeak with a buzzer - a signal that there is zero resistance between the terminals of the transistor.
It is worth considering that with such a quick check, the parts associated with the tested transistor (low-power transistors, etc.) can affect the readings. Therefore, if in doubt - solder and check the transistor separately. It is not uncommon that punctured are just the elements associated with our transistor, and not he. In some amplifiers, for example, such as SUPRA SBD-A4240, MOSFETs are used as output transistors. MOSFET transistors can be tested with a universal tester, since for such purposes a conventional multimeter is not always suitable.
Let's go back to our amplifier. For greater clarity, I will refer to the circuit diagram of this amplifier - the circuit of the CALCELL POP 80.4 auto amplifier. When checking the output transistors for one of them, the Base-Collector (B-C) junction “rang” as broken. In the diagram, it is designated as Q312 (2SA1694) To check the efficiency of the amplifier, I pulled out a faulty transistor and its complementary pair - transistor 2SC4467 (Q311). He turned on the amplifier, but he again went to the defense. So somewhere burned something left. In addition, low-power transistors Q309 (MPSA06) and Q310 (MPSA56) The test showed that the transistor Q309 (MPSA06) has broken both transitions.
Since there was no complementary pair 2SC4467 / 2SA1694 on sale, I decided to replace it with more powerful analogues - a pair 2SA1943 / 2SC5200 manufactured by TOSHIBA. Like that. They are heavy to the touch and inspire confidence.
After installing the new 2SA1943 / 2SC5200 transistors, it turned out that they are large and because of this the board does not fit into the case.
I had to bite a small part of the printed circuit board so that they were tucked into the case and fit snugly to the surface.
After replacing the amplifier began to work properly.
During the electric drive, I noticed that even without load, low-power transistors in the preamps are quite noticeably heated. When playing music with plentiful bass, the heating intensifies. The amplifier worked on two subwoofers (one per bridge).
Perhaps, long-term operation at maximum power led to overheating and failure of the low-power transistor MPSA06 (Q309), and this, in turn, to a breakdown of the BK transition of the powerful transistor 2SA1694 (Q312) in the output stage of the amplifier.
4. Custom case. CALCELL amplifier just bought at the store was brought in for repair. According to the owner, after connecting the power from the ventilation holes of the amplifier, smoke began to flow.
After opening and inspecting the printed circuit board, it turned out that the terminals of one of the MOSFET transistors of the converter have traces of solder paste, solder balls. Here is a photo.
Apparently, a current went through the remnants of solder paste when turned on. Because of this, the rosin in the paste heated up and began to evaporate in the form of a white haze. After that, the amplifier did not turn on due to the solder jumper formed during the reflow of the solder paste. It's no secret that cheap electronics made in China does not pass pre-sale testing. Hence these "bloopers".
Repair of car amplifier Lanzar VIBE 221.
Diagnosis: auto power does not turn on. No LED indication. Judging by the appearance of the printed circuit board, they tried to repair the amplifier, and even the key MOSFET transistors in one of the converter arms were replaced. Instead of the native IRFZ44N, STP55N06 was installed. But the amplifier ordered a long life. Also in the gate circuit of the MOS transistors were "burnt", but serviceable resistors of 100 ohms. When checking the 2SA1023 buffer transistors, which "swing" the IRFZ44N mosfets, it turned out that they were working.
After replacing the TL494CN SHI controller chip, the amplifier worked. Just in case, buffer transistors 2SA1023 and diodes 1N4148 in the base-emitter circuit of these transistors were replaced.
Repair car amplifier Mystery.
Problem: the amplifier turns on, but there is no sound. Car amplifier Mystery 1.300 typical representative of the so-called monoblocks. That is, it is a monophonic amplifier. The declared sound power of the manufacturer is 300W. Such amplifiers are usually used to work on a powerful woofer, that is, a subwoofer or subwoofer.
After opening and examining the printed circuit board, it turned out that several transistors (2SB1367 and 2SD2058) were poorly soldered, there was degradation of the soldering and excessive heating of the soldering spots. Transistors, apparently, are part of the 15V stabilizers in the secondary power circuits. These stabilizers serve to power operational amplifiers and amplifier filters. In another way, this node can be called preamplifier. It is to him that we connect the very “tulips” through which the sound signal from the car radio is emitted. Naturally, if there is no power to the preamplifier, then there will be no sound.
Why did it happen? The fact is that transistors that overheat do not have a radiator, their case is plastic. They are based on their own conclusions. There is no additional fastening. Due to overheating and constant shaking (it is installed in the car), the soldering collapsed and the contact was broken. Therefore, the stabilizers stopped working. A little more and the transistors would just fall out of the mounting holes!
After the restoration of the soldering of the transistors, the amplifier fully worked, but a noticeable heating of the transistors suggested that after a while there would be a repeat.
It was decided to install heating transistors on a makeshift radiator to reduce heat. Also update the soldering of conclusions and make it more reliable. Here is what came of it.
At the same time, neighboring transistors were planted on the radiator, which heated less - to give rigidity to the structure. Since the transistors are in a plastic case and do not have a metal flange, I applied KPT-19 heat-conducting paste to the place of thermal contact with the radiator.
In addition, the all-in-one PCB contained a clearly “swollen” 3300 µF * 63V electrolytic capacitor in the secondary rectifier. In the power supply - inverter, usually 2 electrolytic capacitors are placed, since food amplifier stages bipolar, in the region of ± 28 - 37 volts. The neighboring electrolyte looked better and was not "bloated".
It was decided, just in case, to replace that electrolyte that was swollen with a new one at 4700 µF * 63V (such was available). During the electric drive of the auto amplifier, it turned out that the replaced electrolytic capacitor is slightly heated. It turned out that it was heated by nearby powerful resistors. For reference, the neighboring electrolyte does not have such resistors nearby. This is a clear flaw. As you know, heating has a bad effect on electrolytic capacitors, since the electrolyte dries faster and their capacity decreases.
Repair of car amplifier Fusion FP-804.
Fault: the car does not turn on. There is no indication. After opening, I did not have to search for a reason for a long time. In the converter, all the HFP50N06 MOSFETs (original STP50N06), as well as several 47 Ohm resistors in the gate circuit of some of these transistors, burned out. Also knocked out 2SA1266 buffer transistors.
Instead of burned-out transistors HFP50N06, IRFZ48Ns were installed, 2SA1266 buffer transistors, burned-out 47 Ohm resistors were replaced with new ones, as well as just in case the TL494CN chip-controller.
The device turned on and began to work properly. But my joy was short-lived. Three days later, the owner of the amplifier called me and said that there was a weak monotonous whistle in the rear speakers. A whistle was heard only with the engine running.
The first thought that came to mind was the interference from the generator, which fell into the sound path of the amplifier. This happens with hastily made wiring and the proximity of the supply and signal (inter-unit) circuits. But the wiring and interconnect cables were performed efficiently, as I was convinced. A day later, they brought me a "dead" Fusion FP-804 amplifier with a familiar diagnosis: it does not turn on.
The most interesting thing was that the power indicator "Power" shone faintly. But I did not pay attention to this. After the autopsy, it turned out that again the same MOSFETs were knocked out. So this amplifier was in my pile of scrap - given to the details.
After some time, I decided to restore this amplifier, and I wanted to figure out what was the reason for the massive burn-out of the rather expensive mosfets in the converter. I bought new transistors instead of faulty ones, installed and.
At the first launch, he witnessed an enchanting show. Immediately after switching on, an increasing whistle was heard - the converter started slowly, and then I saw sparks jumping from the center of the toroidal transformer.
Here it is - a malfunction! Breakdown of windings in a transformer. If he hesitated and did not turn it off, he would have completely burned out this batch of MOSFETs.
After that, it became clear why the green “Power” LED was dimly lit with connected power 12V. The current entered the secondary circuit through a breakdown between the transformer windings and the power indication LED was slightly "illuminated". I encountered such a malfunction for the first time. The only way out is rewinding a toroidal transformer.
The schematic diagram of the Fusion FP-804 auto amplifier (aka Blaupunkt GTA-480) is given here.
Repair car amplifier SUPRA.
Car amplifier SUPRA SBD-A4240.
Fault: Turns on normally - "green LED". But when a signal is applied to the sound inputs, there is no channel. The amplifier is silent.
This fault is not typical. For a better explanation of the search and troubleshooting technique, I will refer to the circuit of this amplifier. Schematic diagram of a car amplifier Supra SBD-A4240 (opens in a new window).
Measurements of the supply voltage in the secondary circuits did not give anything - everything is normal. After a quick check, a punctured Zener diode 7.5V was detected (indicated in the diagram as ZD4).
A punched zener diode led to the disconnection of the signal circuits of all amplifiers, since it was installed in the input signal blocking circuit (Q3, Q101, Q201, Q301, Q401, ZD3, ZD4).
This circuit blocks the passage of the audio signal to the inputs of the preamplifiers. The signal is "blocked" for a short time, immediately after turning on the amplifier. This is done in order to avoid a “click” in the speakers.
Since there was no zener diode at 7.5V, instead of a punched one, a zener diode was installed at 5.6V (this led to slight distortion of the signal, later it installed a zener diode at 7.5V). После этого стали работать 3 канала с небольшими искажениями, а 1 канал выдавал сильные искажения с признаками самовозбуждения усилителя. При касании пинцетом входа звукового сигнала ("тюльпанов") в динамике слышалось периодическое "бульканье".
Подозрение пало на блок входных фильтров, тот, что реализован на операционных усилителях - микросхемах KIA4558 (на схеме U1-A and U2-A) Поэтому, чтобы определить, где же кроется неисправность, была разорвана сигнальная цепь, идущая с выхода блока входных фильтров ко входу предусилителя.This is done simply - one output of the electrolytic capacitor is soldered (in the diagram it is C108).
Next, touch the tweezers of the output of the resistor R115 or the output of the base of the transistor Q103. Thus, we apply a signal-to-noise signal to the preamplifier input. Moreover, if the amplifier is working, then in the speakers we will hear a characteristic hum. But in this case, along with the buzz in the dynamics, I again heard the nasty "gurgle". It became clear that the problem must be sought in the preamplifier, and not in the block of input filters.
The search for a faulty element in the preamplifier was complicated by the fact that it was performed on low-power transistors (on the Q102 - Q116 circuit), of which there are quite a lot. Checking these transistors without soldering from the board (for breakdowns of the transitions) did not give a result. Therefore, it was decided to unsolder all the transistors of the preamplifier and check them already more carefully.
This also did not produce a result, although it was possible to detect two transistors 2N5551, which caused distrust. I checked them with a universal tester, and they were once determined to be punched. I had to replace them with new ones. All other transistors turned out to be working, as well as other elements of the circuit: diodes (D3 - D5) and capacitors. BUT! I did not check the resistors!
During an external examination, I noticed that on the case of one of the resistors (on the R124 circuit - 47 Ohms) it was barely noticeable burnout. When checking, it turned out that the resistor is open.
Since the resistor R124 is installed in the emitter circuit of the Q106 transistor (2N5551), its open circuit led to incorrect operation of the amplifier and the same “gurgle”. After replacing the faulty resistor, the amplifier began to work properly. It was also replaced by a new Q106 transistor. As already mentioned, when checking a pair of transistors 2N5551 came under suspicion. Perhaps one of them is the Q106 transistor, in the circuit of which the resistor R124 burned out.
Another malfunction of the same amplifier.
The repair was brought to us by the already known car amplifier SUPRA SBD-A4240 (V1M07) with "torn" electrolytes in the secondary circuits of the converter. To my question: “How did this happen?”, The owner replied that the amplifier was in a car that had an accident. As a result, the amplifier worked properly, but there was an eerie background in the speakers - impulse noise from the converter was doing its job. In place of the native capacitors, new ones were installed, with a capacity of 2200 μF * 35V. The background is gone.
If possible, then, of course, it is better to put electrolytes with a larger capacity (2200 - 4700 uF).
There are cases that it is quite difficult to find a large-capacity electrolytic capacitor. No problem! You can make a composite capacitor from several, the capacity of which is small. Read how to connect capacitors right here.
Other little things.
All active elements - transistors, both field and powerful complementary pairs of transistors are installed on the radiator through an insulating mica strip. Heat transfer paste is used to improve heat transfer.
In some cases, it is necessary to dismantle the printed circuit board from the amplifier housing, which is still a radiator. Naturally, the heat-conducting paste is smeared, soils everything around, dust and dirt stick to it. Therefore, you have to remove it from the radiator and transistor cases, clean the insulating gaskets from mica from it. Occupation is not pleasant.
After repair, everything needs to be restored, as it was. Thermally conductive paste should be at hand KPT-8 or KPT-19. It is better to apply the paste on both sides, both on the metal substrate of the transistor and on the radiator. In this case, the mica will be in the middle and on both sides covered with a layer of thermal paste. I do not recommend applying a lot of paste, the main thing is that an even, thin layer of paste forms on the surface.
I advise you to buy mica on the occasion. For example, I bought a mica plate measuring 10 * 5 cm and a thickness of about 1 mm. Mica can be easily “stratified” with a sharp knife blade. Get a few insulating mica pads. They can be used instead of broken, damaged, lost insulation pads. Mica is easily cut with a knife into plates of a suitable size.