LC III - no audio

[JC8080]

I recently picked up an LC III, when I first powered it on everything worked great, I had video and a startup chime. On about the fifth time I powered it on the startup chime was garbled, and after that it never chimed again. I have also tried headphones, no chime. When I have headphones plugged in and switch the machine on, I can hear a quiet pop like something is initializing. I recapped the logic board and that did not fix the problem. Everything else still works, video is fine, and the machine functions normally other than no audio. I also followed the instructions in the post linked below to check continuity, everything is good. Does anyone have suggestions for further troubleshooting?

Edit: I do not have a PRAM battery, I still tried the PRAM reset as MrFahrenheit suggested in another thread, though I only did it 10 times and not the 11 that was suggested.

LC III - No video, no sound, and weird schematic

Hi everyone! I recently acquired an LC III which I’ve recapped (both the logic board and the power supply). After recapping, the machine will power on, but will not output any video, and only outputs sound via the speaker jack in the back. I get a boot chime which is immediately followed by a...

68kmla.org

 

[Phipli]

I recapped the logic board and that did not fix the problem.

What methods did you use to clean the board? The audio circuit on LCs seems to be incredibly sensitive to cap juice.

 

[JC8080]

What methods did you use to clean the board? The audio circuit on LCs seems to be incredibly sensitive to cap juice.

Good to know. I used a toothbrush and IPA to scrub around the chips near the caps, then cotton swabs and IPA. I haven't looked at the schematics yet to track down the sound chip. I think my next step will be to remove it, check for broken traces, clean thoroughly, and then re-solder. Are there any particular other components I should look at?

 

[JC8080]

Fixed! I removed the sound chip, cleaned the area thoroughly, and did not see any broken traces. I did a continuity check and everything was fine except for pin 3. Both pin 3 and pin 4 go to +8v, but pin 3 had no continuity to any other points with +8v, and also had no continuity with pin 4. It looks like the pin 3 via was damaged by cap goo, I took a very fine pick and poked at the via and a small piece came off. I bridged pin 3 and 4 with solder and the audio came back.

Thanks to @max1zzz and @David Cook for their help in another thread:

LC III schematic question - is this correct?

I am trying to fix a no-audio issue with my LC III, I removed the sound chip to clean underneath and check for broken traces. I used the Bomarc schematic to check continuity and everything was fine except pin 3. Per the schematic both pin 3 and pin 4 go to +8v. Pin 4 checks out, it has...

68kmla.org