This amp cycles in and out of protection due to DC on the outputs. The protection engages quickly so I can not get a measurement on how much DC.
When I opened the cover I found that one of the plastic zip ties that holds one of the output inductors down had been broken and the inductor has been shorting out on the bottom cover AND on the +71VDC bus bar also. It is still connected and not broken at the board. I also noticed R100 had burned open (R101 in similar design amps). None of the output filter capacitors or any capacitors are bulged and none of the outputs are shorted.
So far I have not removed the board from the heat sink, but I have replaced R100 from the top. I have removed every transistor from the audio driver board to check for leakage and found none. With either of the pre-driver transistors out of circuit, the amp will power up and come out of protection as normal. I do have audio reaching the 4565 on the audio driver board.
I'm thinking that inductor is still suspect. Is there anything else I can verify before complete disassembly?
When I opened the cover I found that one of the plastic zip ties that holds one of the output inductors down had been broken and the inductor has been shorting out on the bottom cover AND on the +71VDC bus bar also. It is still connected and not broken at the board. I also noticed R100 had burned open (R101 in similar design amps). None of the output filter capacitors or any capacitors are bulged and none of the outputs are shorted.
So far I have not removed the board from the heat sink, but I have replaced R100 from the top. I have removed every transistor from the audio driver board to check for leakage and found none. With either of the pre-driver transistors out of circuit, the amp will power up and come out of protection as normal. I do have audio reaching the 4565 on the audio driver board.
I'm thinking that inductor is still suspect. Is there anything else I can verify before complete disassembly?
What resistance do you read from the positive output terminal to pin 2 (counting left-right on the solder side of the board) on the driver board?
I can get at each leg of the outputs from the top and none are shorted together.
Positive speaker terminal is directly connected to pin 2 of the driver board.
None of the top windings on the inductor appear to be shorted together, although they have been grinding on the bottom cover for a while. I separated the windings best I could see on the bottom side where it contacted the buss bar.
Positive speaker terminal is directly connected to pin 2 of the driver board.
None of the top windings on the inductor appear to be shorted together, although they have been grinding on the bottom cover for a while. I separated the windings best I could see on the bottom side where it contacted the buss bar.
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Disable the driver board by soldering a bridge between pins 3 and 4 on U5. Drive a signal into the amp. Do you see audio on pins 1 and 7 of the op-amp on the driver board?
If not, desolder and lift one terminal of R80. Does that allow the op-amp to produce clean audio?
If not, desolder and lift one terminal of R80. Does that allow the op-amp to produce clean audio?
Earlier, when I stated I had audio on that op-amp, I was using the RCA shield as ground.
Using the negative speaker terminal as ground, I have audio signal at pin 7 but not at pin 1 even with one side of R80 lifted.
Using the negative speaker terminal as ground, I have audio signal at pin 7 but not at pin 1 even with one side of R80 lifted.
Do you have audio on pin 3?
What do you see on pin 2?
What is the DC Voltage on pin 1?
If you short pins 1 and 2 of the op-amp, do you see audio on pin 1?
What do you see on pin 2?
What is the DC Voltage on pin 1?
If you short pins 1 and 2 of the op-amp, do you see audio on pin 1?
Audio on Pin 3, Yes
Audio on Pin 2, No
DCV on Pin 1, 14.26V. When I checked that earlier, I was using the wrong ground so I glossed over it.
I replaced the op-amp and re-checked for DC on pin 1, there was none. Checked for Audio on Pin 1 and it was present, didn't need to jumper it to pin 2.
I re-installed the end of R80 and removed the jumper on U5. The amp now powers up, comes out of protection and has audio at the speaker terminals.
Audio on Pin 2, No
DCV on Pin 1, 14.26V. When I checked that earlier, I was using the wrong ground so I glossed over it.
I replaced the op-amp and re-checked for DC on pin 1, there was none. Checked for Audio on Pin 1 and it was present, didn't need to jumper it to pin 2.
I re-installed the end of R80 and removed the jumper on U5. The amp now powers up, comes out of protection and has audio at the speaker terminals.
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