I'm trying to repair an AV-10 with a curious fault, which I have seen other people with similar symptoms but no sign of a solution yet. Curious to know if anyone here has any thoughts :
However, I've been tracing through the circuits and reading someone's repair notes made on an AV-8 with a faulty audio switch IC, and given that feeding a signal into the RCA outputs results in output at the speaker terminals, I'm guessing there must be a problem with the audio switch ICs so I was planning to replace those as a start. I've not been able to find any signs of broken/cracked tracks and have tried putting pressure on the boards in different locations and there's no impact. I've found a few resistors and transistors in the power section that have signs of high temp on the board, but they all test ok. I don't have a scope so can't look at the control bus.
- When powered up, the standby light comes on, but the front power button doesn't do anything. The rear power switch operates correctly (ie turns standby mode on/off)
- Pressing the Memory button turns the unit on/out of standby(consistently)
- Pressing the Tuning Mode button turns the unit off/into standby (consistently)
- Pressing other buttons has no impact (power, tuning, input selection, etc)
- When powered up, out of standby mode, the front indicator LED for Video 1 is lit
- Feeding an audio signal into the VCR1, VCR2 or Tape RCA Outputs will result in audio output being sent to the speakers, with adjustment possible via the volume control.
- Feeding an audio signal into the F/R pre-out RCA will result in full volume output at the speakers (not sure if that would always be the case)
- The A/B speaker switching, loudness and tone control circuits are all functioning (scratchy tone switch, which I will fix)
- Disconnecting boards other than main board and front PCB has no impact
However, I've been tracing through the circuits and reading someone's repair notes made on an AV-8 with a faulty audio switch IC, and given that feeding a signal into the RCA outputs results in output at the speaker terminals, I'm guessing there must be a problem with the audio switch ICs so I was planning to replace those as a start. I've not been able to find any signs of broken/cracked tracks and have tried putting pressure on the boards in different locations and there's no impact. I've found a few resistors and transistors in the power section that have signs of high temp on the board, but they all test ok. I don't have a scope so can't look at the control bus.
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So I've swapped out the audio switch IC's, now there is no audio path working, and the on/off function is still done by the two switches I mentioned. I guess it's off to the junk heap...
I guess this ain't the right forum for fixing commercial products but in case anyone comes across this and is interested...the source input selection on the AV-10 is done via a resistor ladder network with three rails. The rail that the standby power switch is on was at 1.2v while the others were at 4.8v. All of the resistors measured correctly, and there was a 470pF capacitor in the circuit that measured ok but had corrosion on it from a supercapacitor physically next to it that had leaked. So I replaced it, and everything started working again. The part was 17 cents.