Subwoofer amplifier MIK

[Nite]

The amp is still heating up with the leftmost driver (the original part that I didn't replace before) out of the circuit, so I guess the fault must be somewhere else? How do I check transistors for leaking? Also, the trasistors at the bottom Q22 (TIP42C) and Q23 (TIP24C) get warm as well, what purpose do they serve in the amp? Could it be that the diodes next to the drivers are faulty? Thanks for all the help.

[Nite]

The leftmost driver kd600K doesn't appear to be leaking. B->E is 0.6V, the other way around is OL, B-> C is 0.6 and the other way around is OL as well.

[Perry Babin]

When you check for leakage, you also need to check with the meter set to ohms/resistance. The diode-check function isn't sensitive enough to see minor leakage.

[Nite]

OK, B->E reads 23 M ohms(red probe on Base and black on Emitter), the other way around is OL. B->C reads 22 M ohms(red probe on Base and black on Emitter), the other way around is OL. Do you suggest I should check other transistors in the audio section the same way?

[Perry Babin]

That transistor appears to be OK. Since no schematic is available and there aren't many transistors in the audio circuit, checking each transistor may be the best way to proceed. Confirm that each transistor has two good junctions and that there is no leakage.

[Nite]

That's fine, I will remove the transistors one by one for checking. Do you have any good tips to get that yellow glue off? It really slows down the whole process.

[Perry Babin]

I'm not sure for that particular fixative but for many fixatives, heating with a heatgun will soften it and allow you to peel it off of the board.

[Nite]

I replaced 2sa1023 and 2sc1027 with new ones and the DC voltage on the speaker connections dropped from 0.39V to 0.1V, so this means that at least one transistor is still passin DC? I have removed and checked most of them and they seem fine, but maybe I missed something. I'll test the rest of them tomorrow, but if this won't lead me anywhere, is it okay to replace 2sa1266 with 2sa1015 and 2sc3198 with 2sc1815 in the audio section. I have another amp for parts.

[Perry Babin]

Those should be good subs but only replace parts that you know to be defective.

The offset could mean that you have a leaky transistor but it can also be caused by mismatched transistors in the differential amplifier stage of the power amplifier.