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LC III lost sound

Posted by: Verault on 2022-10-13 07:08:02

So my LC III doesnt make a sound anymore. I have been trying to find the soundchip to no avail. I was able to get sound back on my LC II by using deoxit and a toothbrush on a couple areas which had some whitish buildup on IC pins. I tried this on the LC III but still no sound.

Board was recapped a couple years ago and has been fine otherwise. Any ideas?

Posted by: paws on 2022-10-13 07:19:29

Is it only the internal speaker or also using the output jack?

Posted by: MrFahrenheit on 2022-10-13 07:35:21

I had this problem back in the day. Apple service outlet told me to power on fresh holding PRAM reset keys for 11 restart cycles to clear corrupted PRAM. It solved the problem which quite surprised me.

Posted by: Verault on 2022-10-13 09:00:04

I havent tried the audio out jack to be honest. I will try that.

I dont use the system with a PRAM battery in it though (and I didnt use a PRAM battery when the sound was still working). Do you think that fix may work anyway? Waht are the PRAM reset keys?

Thanks guys

Posted by: MrFahrenheit on 2022-10-13 09:10:52

I havent tried the audio out jack to be honest. I will try that.

I dont use the system with a PRAM battery in it though (and I didnt use a PRAM battery when the sound was still working). Do you think that fix may work anyway? Waht are the PRAM reset keys?

Thanks guys

Its possible the PRAM has become corrupt. I’d still try resetting it.

The keys to hold down before switching on are:

Command Option P R

I usually hold half down with one hand, switch on and quickly place fingers on other half before the system skips it.

Posted by: joshc on 2022-10-13 09:47:13

Try the audio out jack, could just be a bad speaker.

How well was the board cleaned when the caps were done? Could be dirt on the sound chip.

Posted by: Verault on 2022-10-13 09:57:58

Ok So I tried headphones and I do get sound out via the audio out. There is a hot popping though almost as if there is a short.

I tried the PRAM reset in excess of 11 times and it still makes no sound via internal speaker.

Board was cleaned pretty well. This board didnt have much residue as compared to the LC1's and II's I repaired. The board is pretty clean.

JoshC I tried a spare speaker as well.. I have a small heap of good speakers.. No change with that either.

Posted by: Skate323k137 on 2022-10-13 10:10:24

Did you do the recapping yourself? Or do you completely trust the person who did the work?

Posted by: Verault on 2022-10-13 10:18:07

I did the work. And like I mentioned the sound was working up until this year. Then one day it was just silent.

Posted by: Verault on 2022-10-13 10:36:57

Ok this is weird. The sound just came back. After about 3 or 4 restarts from doing the PRAM reset. I could be wrong but it sounds slowed down to me but its there.

Posted by: 3lectr1cPPC on 2022-10-13 10:58:12

Did you ever remove the sound chip? Maybe some crud has been lying under it and it’s now causing a short or an intermittent trace/via.

Posted by: Verault on 2022-10-13 10:59:28

it could be crud, like I said its pretty clean and i used deoxit with a toothbrush and I dont see anything.

Posted by: 3lectr1cPPC on 2022-10-13 11:00:13

Wouldn’t hurt to remove it if you’ve got the skills to do so.

Posted by: Verault on 2022-10-13 11:02:18

Honestly I have no problem removing an SMD IC like this. But my track record with sound chips failing on old macs makes me not want to touch it. Too many color classic repairs and pulling chips on and off. Ill just run it until the issue presents again.

Posted by: David Cook on 2022-10-13 11:08:58

Follow these steps to determine if there is a problem with the jacks or any of the traces:

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

Let me know what you find.

Posted by: Verault on 2022-10-13 11:16:09

This is good stuff David thank you. I will run these tests.

Posted by: Verault on 2022-10-13 11:20:33

Completely unrelated but what is meant to connect the the strange tiny connector at J7? I see this on a bunch of boards and have no idea what its for.

Posted by: Hellion on 2022-11-13 19:52:37

Completely unrelated but what is meant to connect the the strange tiny connector at J7? I see this on a bunch of boards and have no idea what its for.

Accordning to 'mmu_man', that is a video connector for passing through signals from a PDS card. Source: https://68kmla.org/bb/index.php?threads/reverse-engineering-the-macintosh-lc-iii-logicboard.38814/

Posted by: Verault on 2022-11-13 20:00:51

Accordning to 'mmu_man', that is a video connector for passing through signals from a PDS card. Source: https://68kmla.org/bb/index.php?threads/reverse-engineering-the-macintosh-lc-iii-logicboard.38814/

Interesting. I never owned a PDS video card.