Berea, OH
This is a multi-stage audio amplifier on the aux power supply board. Which "amplifiers" did you replace? Do you have an oscilloscope and know how to use it to troubleshoot audio amplifiers?
(Topic ID: 230798)
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Quoted from robx46:I have a logic probe. & no I don't know how to troubleshoot them but I'd like to! The tda2040 are good on aux power board, I thought those were the only amp that would cause nothingness but now that you mention it I forgot about the 3403 ic. I already replaced those a while back on the main board, but I do have new aux sound & aux power boards that I could install new ones on.
A logic probe won't do you much good for checking the audio path. An oscilloscope lets you see audio waves, so you can find where the signal is getting lost. If you have new aux power board, did you try to sub that in? (assuming it works)
amp (resized).pngQuoted from robx46:My old aux power board had 12v dc leakage to the speakers. I never could track down the cause. New (old) board from PBR is in there now. I actually do have an oscilloscope ordered since I found one cheap online a couple weeks ago so maybe it will come in handy here. In the meantime I may try new 3403 on the aux power board & see what happens.
If you have not done so, I would suggest swapping P2 cable inputs pins 1 & 3 to the aux power supply board. If the problem remains the backbox speakers dead, then you definitely have a problem with that board. If the backbox speakers work and the cab speaker stops working, then the problem is upstream at the sound board.
Quoted from robx46:I did that & still no sound from the top speakers
If you switched the inputs and the dead speakers are still the top speakers in the backbox, then you definitely have a problem with the amplifier circuit for that channel on the aux power supply board. Could be a lot of things besides the ICs, open caps etc...
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