Hi. I am repairing a cheap blown amplifier which has two pairs of C5198 / A1941 output power transistors. It belongs to a friend of mine. Previous signs of a repair, someone soldered wires instead of fuses. A couple of 100 ohm 1/2 watt resistors, a 1/4 watt 1k ohm resistor, 2 x 5 watt resistors, A940 transistor, C2073 transistor, D669 transistor, 2 x C5198 2 x A1941 transistors were blown / shorted. The output transistors were shorted on all three pins, very bad since the wire fuses did not blow. I replaced all the damaged items. I failed to get the A940 and C2073 transistors, I got TIP41C and TIP42C, will they work? I also replaced D669 with BD139??? I tested it and it blew both fuses and 2 output transistors. I have tested everything, the bridge diodes, resistors, diodes, small transistors (5551 , 5401) all are fine. But somehow it keeps blowing fuses. There is one item I have not tested, an ic : upc1237 could it be causing this? Let me know. Thanks
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The upc1237 is a dual channel load protector and has nothing to do with your described fault.
Before replacing the blown semiconductors and powering it back up to do the same, I would fault find it first.
Transistors blow for a reason, not on their own.
Before replacing the blown semiconductors and powering it back up to do the same, I would fault find it first.
Transistors blow for a reason, not on their own.
Are the fuses before the large filter caps?
I have seen shorted electrolytic filter caps before.
A simple ohm meter test across the cap will let you know.
If it reads short, remove the cap and verify, as the short could be elsewhere.
Also what value are the fuses and are they time delay types?
I have seen shorted electrolytic filter caps before.
A simple ohm meter test across the cap will let you know.
If it reads short, remove the cap and verify, as the short could be elsewhere.
Also what value are the fuses and are they time delay types?
Yes the fuses are before the large filter caps. There is no short on the caps. The fuses are 12A. Let me check for shorts on other electrolytic caps perhaps.
It is unlikely that you will fix an amplifier by replacing another part and see what happens. You have to test every part step by step. You need a schematic or reverse engineer the PCB. You need to test all the bias and drivers as well as outputs and disconnect them to test the power supply. Some people use the light bulb/ resistor to limit the current but that may not protect smaller devices like the drivers. Amp failure often means the drivers and bias transistors are also blow and just replacing the output transistors will just blow up the new parts in an instant.