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Macintosh LC recapping woes


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So a while ago I got a Macintosh LC, power supply was dead but in the meantime I was able to get it working by connecting it to an ATX power supply. It had no sound but otherwise seemed to work fine. Obviously the capacitors were at fault there, so I got new capacitors and set to work...

 

... except now the damn thing won't work anymore. I checked my capacitors a billion times, they're installed correctly and the soldering is good. I cleaned the motherboard as much as I could. Still nothing.

 

Actually it's outputting a video signal at the correct resolution, but that's about it. The screen stays black, no audio, no sign of life.

 

I'm thinking of checking and redoing my capacitors one by one incase something got stuck under one and is shorting things... but first want to see if I can save myself that trouble. Also, should I also replace C9? On my board it's a big 2200µF capacitor, and it looks good (no leaking gunk, no bulging), so I didn't replace it. Could that be wrecking havoc?

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  • 2 weeks later...

No change as in No Boot and No Video?

 

You are going to have to go in with a multimeter and check for a broken trace around the caps. Also look carefully as some traces goes under a cap but not connect to it but connect to other areas; the Cap Goo can eat away at these traces as well. You may have to remove the cap to inspect the path of the trace but that maybe on 25% of all the caps and traces you may need to inspect. If the trace is broken, just run a thin wire from its start to end points.

 

A large magnifying glass or a pair of magnifying glasses would be helpful to the cause.

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I redid my soldering with proper cleanup and flux and all. Did the difference, now it's working reliably. I did check the traces around capacitors, there was one broken trace, which may or may not have been there before, but it was quickly taken care of.

 

I also had to add a couple bodge wires to fix audio, there were some broken traces. Pin 4 of UC9 was disconnected. Also for some reason the grounds for the audio chips were disconnected from the rest of the grounds, but I couldn't find where the break was.

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  • 1 month later...
On 11/26/2020 at 10:52 PM, Arisotura said:

Also for some reason the grounds for the audio chips were disconnected from the rest of the grounds, but I couldn't find where the break was.

I actually learned from this video that this is by design -- the analog ground goes through the RF shield, which eventually connects to the power supply's ground. Obviously this only works if the motherboard is seated in its case...

 

I removed the ground bodge I had done, and, sure enough, audio on my LC still worked fine.

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