68kMLA Classic Interface

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Color Classic II without audio

Posted by: dangil on 2020-09-04 14:57:15 I have a Color Classic II that powers up, but has no audio already recapped it while checking the board, I found that most of the ground pins on the capacitors I replaced have continuity with the ground on the motherboard connector near the 5V and 12V lines, but they don't have continuity with the ground on the scsi external connector or the audio plug outer shell for example all the audio capacitors have this continuity, but seem isolated from the same ground near 5V and 12V it seems the board has 2 different grounds, but I can't imagine how this would happen already cleaned the board very very well... all replaced capacitors have continuity with their respective grounds basically audio caps are grounded with outer shell, and the rest of them are grounded with the power supply. it's as if there were something in between, because I can read a voltage drop between them.. it's not totally open any tips on how to diagnose this weird ground issue?

Posted by: Oberlehrer on 2020-09-04 15:36:11 Having separate digital and analog grounds is not uncommon where I come from; no idea if this is also done with the Classic II though. Usually those are then tied together at a single point in or near the power supply (unless there are also separate supply lines for digital and analog IC's). Perhaps that point where the grounds are tied together is missing.

Posted by: bibilit on 2020-09-04 17:53:00 The chip sound is near four caps.  Probably contaminated by goo.  Best option is to remove the chip, clean underneath and put it back.  Have been there lately.

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