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Macintosh LC Quiet sound after recap?


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I recapped my Macintosh LC, which after a wash before recapping, worked perfectly fine, aside from its speaker being a little bit quieter than one of my other LC II or LC 475.  After the recap, it's sound is very very low, you can barely even hear it, even if you put your head close to the speaker. I cleaned around the sound chip many times with IPA, all traces look good. What happened? And what can I do to fix it? I was thinking of removing the chip with a hot air station to clean and check for broken traces under the sound chip, but I want to see what you guys have to say first. Thanks.

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20 hours ago, cadenya said:

I recapped my Macintosh LC, which after a wash before recapping, worked perfectly fine, aside from its speaker being a little bit quieter than one of my other LC II or LC 475.  After the recap, it's sound is very very low, you can barely even hear it, even if you put your head close to the speaker. I cleaned around the sound chip many times with IPA, all traces look good. What happened? And what can I do to fix it? I was thinking of removing the chip with a hot air station to clean and check for broken traces under the sound chip, but I want to see what you guys have to say first. Thanks.


Just out of curiosity, did you use a good PRAM battery, and reset PRAM by holding Command Option P R while switching on and what you perceive to be 10 full reboot cycles ?

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20 hours ago, cadenya said:

No I did not, I had to do 10 reboots?


Hold the keys. Switch on. Wait until it does at least 10 cycles before letting go. 
 

It seems like it’s extreme. It’s exactly what Apple did on my Q605 back in 1994 when my sound stopped working. I took it in under warranty and an hour later I got it back with a bill for $130. I asked why and they said corrupted PRAM was the cause and told me the 10 reboot cycle clears it more than just one and 3 Cycles. I never forgot, after having to pay $130. 

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20 hours ago, cadenya said:

Wow, didn't know that. So I just hold the keys and wait for something like 2 minutes? Since I can't really hear the sound. Or do I unplug everything except the logic board?

Hold down keys. Turn on. You should see a graphical indication of the reboot. If not, then wait about 2 1/2 minutes while holding the keys. Turn off. Turn on. 

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20 hours ago, cadenya said:

No, it did not work. I did it over 15 times. Should I remove the chip to check for broken traces/clean under it? Or is it not worth it?


Well it was worth a shot. That step is free and painless. 
 

Maybe someone else here will have a suggestion. 

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Sorry to sound like Mr. Obvious, but if it worked before your re-cap, I'd double-check your re-cap job. I'm not too familiar with that mainboard, but 1 or more caps may be an audio filter cap and perhaps you used the wrong value when replacing. Did you check for damage to the board after removing the caps? Did you clean the board thoroughly after removing the caps and before replacing them? Maybe you damaged a trace while soldering?

Edited by mattsoft
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Yes, I checked everything. I removed the chip, and checked every single trace on the chip area. The chip is soaking in some IPA right now, I'll put it back on in a few minutes. Guess the chip is bad? But wouldn't there be no sound at all if it were? 

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<dunno> It's probably one of these 3: (1) bad audio chip, (2) bad trace(s) somewhere, (3) bad cap. If you are sure there are no bad traces and your caps are all good, then I guess that leaves bad audio chip. Strange that it would fail while re-capping. Maybe you hit it with too much heat and damaged it? </dunno>

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On 4/12/2021 at 9:51 AM, cadenya said:

Yes, I checked everything. I removed the chip, and checked every single trace on the chip area. The chip is soaking in some IPA right now, I'll put it back on in a few minutes. Guess the chip is bad? But wouldn't there be no sound at all if it were? 

 

Did cleaning and re-soldering the sound ship fix the problem? I had the essentially the same experience with my LC II: sound but lots of weird noise before motherboard wash and recap; very faint sound after, but an otherwise functional computer) and I would love to know if this fixed it for you.

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Nope, it actually made it worse. I thought I killed the sound, but it's just barely audible if you put your head to the speaker hole. I think the chip is damaged, and removing it and cleaning made it worse. Because the only way it could have gotten worse after a recap was my cleaning, I cleaned the board in IPA and I guess it made the chip worse.

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Disappointing to hear that; I was hoping that would be the solution to both of our problems. I am also planning on cleaning under and replacing the op-amp chip as well, in case the signal from the sound chip is fine and there is actually a problem between audio output pin 10 of the sound chip and the speaker.

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Yeah, this sounds like a bad sound chip (sorry, couldn't resist). A lot of the Mac sound chips are available on utsource.net - look up the part number and see if they have it.

 

Also worth double-checking with a spare speaker from another Mac to rule that out...

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