Hello,
I'm working on a Denon PMA-500 (~30yo?) integrated amp as a project piece, and trying to walk back the trail of destruction that happened when I shorted TR211's G-C, which somehow caused zener D202 to short. I replaced the zener, but now there's an overvoltage situation on the negative side causing all the input selection lights to glow (the selected one glows a little more).
The voltage drops across R201 and R202 (coordinates 5G on the schematic) are almost double what they should be, and they are spicy (>100C). Why is there so much current? The DBT glows only faintly.
Pin 12 of IC3 is at -23.2v rather than -14.6v, the other pins seem within spitting distance of nominal. I hope nothing is fried in the IC. It's soldered in, so difficult to test out of circuit.
Checked TR208-212 for shorts, they seem ok.
I am a stumped newb hoping that some internet stranger might be able to point me in some direction. I've spared no effort in annotating the service manual schematic, certainly my greatest masterpiece in this discipline so far.
Any pointers to help me troubleshoot this circuit more effectively?
Best regards!
Denon PMA-500v service manual
I'm working on a Denon PMA-500 (~30yo?) integrated amp as a project piece, and trying to walk back the trail of destruction that happened when I shorted TR211's G-C, which somehow caused zener D202 to short. I replaced the zener, but now there's an overvoltage situation on the negative side causing all the input selection lights to glow (the selected one glows a little more).
The voltage drops across R201 and R202 (coordinates 5G on the schematic) are almost double what they should be, and they are spicy (>100C). Why is there so much current? The DBT glows only faintly.
Pin 12 of IC3 is at -23.2v rather than -14.6v, the other pins seem within spitting distance of nominal. I hope nothing is fried in the IC. It's soldered in, so difficult to test out of circuit.
Checked TR208-212 for shorts, they seem ok.
I am a stumped newb hoping that some internet stranger might be able to point me in some direction. I've spared no effort in annotating the service manual schematic, certainly my greatest masterpiece in this discipline so far.
Any pointers to help me troubleshoot this circuit more effectively?
Best regards!
Denon PMA-500v service manual
The most glaring voltage I spot is -22.8V at the base of TR208. If the regulator were working, the base would measure about -0.6V. Perhaps the base-emitter junction is open, or perhaps open board traces at TR208.
Good luck!
Welcome to the forum!
Good luck!
Welcome to the forum!
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Ah, sure enough I pulled TR208 and it's not passing the DMM test! Now let's see what's in the parts bin...
Thank you
Thank you
Epilogue, that seems to have been the last piece of the puzzle and the amp is currently singing with correct voltages everywhere. I replaced the faulty 2SA1015Y with a KSA1013YBU from the bin which has higher maximum everything and ballpark-similar gain. Max collector and emitter cut-off currents are much lower but it doesn't seem to hurt anything. I don't think any audio signals are going through this, just seems like it's delivering power to other sections.
I also found some generic 2SA1015 clones on DigiKey but I think I'll leave the current one in as it seems to be working fine. I'm new to this, so getting a broken $20 amp to sound this good is really satisfying!
I also found some generic 2SA1015 clones on DigiKey but I think I'll leave the current one in as it seems to be working fine. I'm new to this, so getting a broken $20 amp to sound this good is really satisfying!
