On Wed, May 16, 2018 at 4:11 AM, richs19@... [cgs_synth] <cgs_synth@yahoogroups.com> wrote:I'm troubleshooting a CGS85. I was going through the calibration procedure and the first two channels worked fine. I was using an input of 4.2V and was able to calibrate the outputs to match the inputs.
When I got to the third (the bottom on the wiring diagram - furthest from the power connector) the output voltage could not be raised above 1.2V. Even more strangely is that when I measure the input voltage when the 1/4" jack is inserted in the input socket, the voltage drops to .38 Volts.
It's like there's something in that section of the circuit causing a problem with the actual input signal. All the other channels work fine. I'm comparing the module to a working CGS85 built earlier and all of its inputs match its outputs.
I've re-flowed the solder. No connections look bad and I can't find any obvious bridge solders or wiring faults.
Any suggestions would be greatly appreciated!
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Message
Re: CGS85 Bottom Channel Problem
2018-05-15 by Ken Stone
Check for diodes that are in backwards would be my first guess. If your chips are in sockets, swap the "bad" one to the working unit and see if it works correctly. Check your other component values. If it is none of those, have a very close look at the PCB itself, to see if there are any shorts hidden under the solder mask. It is VERY rare, but does happen occasionally.
Ken