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audio output troubleshooting

BHTek1

New Member
I may never get this solved, but here goes: I have a synthesizer with perfect audio from the onboard speakers, but in the stereo jacks for TS-cable output, one channel has a loud shriek (all static, no desired signal) and the other has no output at all. The shrieking channel does not respond to volume controls; it is at a screeching, full-on level all of the time.

Problems are that the unit is so old that: a) the manufacturer will not dispatch repair personnel, b) standard electronics parts for it are no longer available, c) tech manuals are limited to authorized service centers, d) the unit is too big to transport to a center even if they did agree to work on it. Everything else on the unit is in perfect condition (I can easily replace the mechanical parts), and I don't want to give up on it. There is only one main circuit board, but without schematics or even diagrams of any other sort, I would have to resort to a crude form of "reverse engineering", basically doing exploratory digging around. That would likely risk ruining the entire circuit board and without it, the unit would be rendered worthless and unrecoverable. At the very least, I would only risk very careful connections up to an oscilloscope to read signals until (and if) I can locate the fault(s). If the integrated components are surface-mount type, then "game over".

I suspect that, given the general nature of audio circuitry, late-stage op amps and their associated components might be the most likely cause of the failures. Comment is invited.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Post the Make, model and as many detailed photos of the circuit board as you can, both top and bottom sides.

There is a fair chance someone on here will be able to help!
 

shokjok

Member
Reverse engineering trick: remove the PCB and place it on a copier. Then align both sides to get a connection routing diagram similar to what is found described on electronic patent descriptions for like products. When all the lines are sketched, craft a schematic from each drawing.
 

unclejed613

Well-Known Member
Most Helpful Member
remove the PCB and place it on a copier.
the component side will often be a blur with this method.... if it's a double sided PCB that's not a good way to do it...
 

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