Hello. I found in garage an old amplifier. Opened it and saw that all of IRFZ44N transistors is blown up. I replaced them, was ready to test it. Connected amp to battery and after 1sec 3 of 6 IRFZ44 transistors blow up again. I dont know ehat is wrong. I tested others transistors and they seems to be good, if i test the them correctly. Thanks!
When i try to power amp with psu, the psu turns off immediately, it means that somewhere is short circuit?
When i try to power amp with psu, the psu turns off immediately, it means that somewhere is short circuit?
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For the group of 4 transistors including Q37 and Q40, find the two that have their collector terminals connected to ground. Pull those two and check them (for shorts AND for open junctions). Do NOT apply power with those transistors out if the circuit.
Thanks! Q40 is faulty, there is short. Will need to replace it. Now my amp need to be working again? Thanks again.
Generally, a shorted PNP transistor won't blow FETs. It will, however cause the complementary NPN transistor to open. Check the other PNP for open junctions.
i tested Q38, its the same transistor (A1015) i think its faulty too because multimeter shows 0.99V when i tested it. So i found 2 faulty PNP transistors. In picture can see these 2 faulty transistors where is square. So they can or cant blow up that irfz44? Sorry if im wrong. Im 18 years old guy who want to repair and study new things.
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I'd replace all 4 of those driver transistors unless you can be absolutely sure that the NPN drivers are 100% OK. All 4 drivers have to be in good working order. If any of the 4 are defective, it can cause the power supply to be unreliable or to fail shortly after power is applied.
Replace all 4 driver transistors & the 100R resistors. ALL the IRFZ44 [from the same manufacturer] clean very good the carbon on the PCB.
before you connect it to the Power again [12v] check all Output power transistors if they are ok [not shorted] if you have power supply with current meter take a llok when you connect the remote wire if the current is more then 0.8A-1.2A if so there is still somewhere problem. if it's around the 0.8A touch the IRFZ44 transistors to feel if they coming HOT. not hot? so every thing is OK
before you connect it to the Power again [12v] check all Output power transistors if they are ok [not shorted] if you have power supply with current meter take a llok when you connect the remote wire if the current is more then 0.8A-1.2A if so there is still somewhere problem. if it's around the 0.8A touch the IRFZ44 transistors to feel if they coming HOT. not hot? so every thing is OK
In 80% of cases, when the amplifier is designed well, if there are any shorted transistor, the amplifier turns on and go instantly in protection, so you have the right time to save the new mosfet that you have just installed.
If it is an excessively economic amplifier, the protection will not be fast enough, IRFZ44N will be shorted again.
You should also check for any short between the output transistors. But if you prefer, you use a 5A fuse or a 10w 12v car light bulb in series with the positive supply.
If the light bulb turn on and remain it, there is one or more shorted output transistor or other different issue, Otherwise, if the light turn on and rapidly turn off, probably is all ok.
If it is an excessively economic amplifier, the protection will not be fast enough, IRFZ44N will be shorted again.
You should also check for any short between the output transistors. But if you prefer, you use a 5A fuse or a 10w 12v car light bulb in series with the positive supply.
If the light bulb turn on and remain it, there is one or more shorted output transistor or other different issue, Otherwise, if the light turn on and rapidly turn off, probably is all ok.
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i replaced all 4 driver transistors and checked 100R resistors, the are fine. Checked Output transistors, they are not damaged too.
Because of my english and knowledge I dont understand where i need to put car bulb to check for faulty transistors? There is a short somewhere, because when i connect amp to PSU it turns off immediately.
Thanks!
Because of my english and knowledge I dont understand where i need to put car bulb to check for faulty transistors? There is a short somewhere, because when i connect amp to PSU it turns off immediately.
Thanks!
The current limiter (resistor or headlamp) is inserted in the B+ line feeding the amp.
You can't do anything else until you replace the driver transistors.
The following is from the basic repair page (link in sig line below)
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.
You can't do anything else until you replace the driver transistors.
The following is from the basic repair page (link in sig line below)
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.
Dorozko
maybe you have problem at the Transformer or maybe the TL494 not OK.
send the amplifier to me i will fix it for you 🙂 🙂 🙂
look this is very simple amplifier it's not sophisticated model and BTW there is no any protection for the Power Supply transistors like MarioRestucci say all the "Protection" that most of the time not work fine is at the output stage and the input ground.
maybe you have problem at the Transformer or maybe the TL494 not OK.
send the amplifier to me i will fix it for you 🙂 🙂 🙂
look this is very simple amplifier it's not sophisticated model and BTW there is no any protection for the Power Supply transistors like MarioRestucci say all the "Protection" that most of the time not work fine is at the output stage and the input ground.
this is the cheapest amplifier i saw till now. when i looked deeply i saw that there is no gate voltage limit resistors. and the TL494 is connected directly to the mosfet drivers. i am pretty sure that the TL494 internally short
If your bench power supply can power down when there is a high absorption sudden, most likely it happens because the amplifier has some other problem.
Most likely the main cause that at the beginning he did burn the old IRFZ44N, are definitely one or more output transistors which, in the short time, have put serious effort the internal power supply unit, doing warm up excessively IRFZ44N that eventually they have succumbed.
My advice is to do a real test:
Take note of the location of all of the output transistor; you will need to temporarily remove them all.
After removing all of the output transistors, turn on the amplifier.
If the amp turns on properly and the new IRFZ44N not heat up, it means that there is certainly some output transistor shorted (that may have also caused other types of damage, for example, the driver stage of the short-channel or the differential stage).
We have to go step by step, but this is already a great step, because it allows you to figure out if its power supply has a problem or not!
Most likely the main cause that at the beginning he did burn the old IRFZ44N, are definitely one or more output transistors which, in the short time, have put serious effort the internal power supply unit, doing warm up excessively IRFZ44N that eventually they have succumbed.
My advice is to do a real test:
Take note of the location of all of the output transistor; you will need to temporarily remove them all.
After removing all of the output transistors, turn on the amplifier.
If the amp turns on properly and the new IRFZ44N not heat up, it means that there is certainly some output transistor shorted (that may have also caused other types of damage, for example, the driver stage of the short-channel or the differential stage).
We have to go step by step, but this is already a great step, because it allows you to figure out if its power supply has a problem or not!
In post 14, I started typing before you posted.
Pull the rectifiers to see if the current draw decreases.
Pull the rectifiers to see if the current draw decreases.
In these types of amplifiers, it is better to remove the output transistors instead of the rectifier diodes; the reason is simple:
The preamplifier stage is operated by the main rails through the use of a resistor and a zener diode (in the best of cases, is used a pair of LM7812-15 regulators and LM7912-15) THEREFORE, if there was a problem in the preamplifier stage, removing the diodes, it would not be possible to find it and fix it.
Otherwise, if after removing the output transistors, the problem persists, I could think of other problems.
The preamplifier stage is operated by the main rails through the use of a resistor and a zener diode (in the best of cases, is used a pair of LM7812-15 regulators and LM7912-15) THEREFORE, if there was a problem in the preamplifier stage, removing the diodes, it would not be possible to find it and fix it.
Otherwise, if after removing the output transistors, the problem persists, I could think of other problems.
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