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LCIII, 475, Color Classic, Sound Chip1

Plasticoat

Well-known member
Hi, been a while,

I have been chipping away at certain projects, and life goes past, some wins. Some losses!

but as you all know we get to thinking about the wins that do not function as they should.

I am steadily building a small pile of PCB’s that now function but have no sound, all of them are LC derivative’s , late 90s

as I do not have a scope, my mind twists , damn I need a scope, shucks that’s so much money!!

so I got to soaking boards after removal and replacement new and old chips, some had no change, others had a second life, but not for long, others have a garbled Output.

so now I’m just going to continue on the path that I have be on, however I read a small thread the other day that might give hope to others and me,

just need advice from you guys, as a hive things can get solved, I know how it is, we do not like giving up that special info, that special knack we have to fix something,,

hoping that sound will spark that fire for us all!!
 

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Phipli

Well-known member
Hi, been a while,

I have been chipping away at certain projects, and life goes past, some wins. Some losses!

but as you all know we get to thinking about the wins that do not function as they should.

I am steadily building a small pile of PCB’s that now function but have no sound, all of them are LC derivative’s , late 90s

as I do not have a scope, my mind twists , damn I need a scope, shucks that’s so much money!!

so I got to soaking boards after removal and replacement new and old chips, some had no change, others had a second life, but not for long, others have a garbled Output.

so now I’m just going to continue on the path that I have be on, however I read a small thread the other day that might give hope to others and me,

just need advice from you guys, as a hive things can get solved, I know how it is, we do not like giving up that special info, that special knack we have to fix something,,

hoping that sound will spark that fire for us all!!
First thing to check are the caps, replace the electrolytics, and check any tantalum caps in the sound circuit to make shure they're not shorted out.

I haven't fixed my sound yet, I think I have a short somewhere. Latest theory anyway :)
 

AwkwardPotato

Well-known member
Assuming you've checked the easy things, e.g. caps, rotten traces, whether or not you get sound from the headphone jack...

Many of these LC-derived designs use a 78L08 for the sound IC's (DFAC) analog supply and it's prone to being attacked by cap goo. It should have +12V on one side and +8V on the other. There's also a power amp near the sound IC (MC34119 on the LC I-III, although I believe the Color Classic amp is on the analog board). I have encountered a couple of extremely corroded LC-series boards where even after recap/thorough cleaning, the audio output was noisy and crackly -- reflowing the joints didn't help, it was fixed by replacing the amp.

If the DFAC (II) ultimately turns out to be dead, it's worth noting that it's output section is nothing more than a filter, almost all of the sound generation is done within the V8/Sonora/Spice/etc. Ought to be relatively straightforward to replace it with something like a Sallen-Key low-pass filter implemented with an op-amp, although you'd lose the sound input functionality.
 
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