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LC 1: no chime, no display, fan spins (w/ photo)

9166188

Well-known member
Got a LC w/o a working PSU, but the board looks decent. So, an ATX PSU is used instead to provide 5V and12V. Sadly the machine turns on without any sign of life except the spinning fan.

I have soaked it in hot bath and have it fully recapped already but still no change. I had tried with and without battery, with and without RAMs. Still nothing happens. No sound, no video.

Any ideas? I probed the legs of each capacitor and found some have low voltages (-0.7V, 0.9V, 1.5V, etc) and some registered no voltage at all. Would these help to pinpoint where the problem may lie?

Screenshot 2022-01-15 at 6.15.40 PM.png
 

joshc

Well-known member
I see gunk/cap goo around the legs of various ICs. How did you clean the board?

The Egret (UD8) and Apple Sound Chip/DFAC (UB10) need to be clean for a successful start.

Even the legs around the CPU don't look that clean, maybe its just the photo but it looks like it could be cleaner.

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9166188

Well-known member
Thanks a lot for the detective work! I soaked it in hot water with detergent for some hours. And brushed the board especially around the legs. I will give it another go. Is vinegar a better solvent in this case?
 

mdeverhart

Well-known member
I usually use a cotton swab with some rubbing alcohol to remove cap goo. A toothbrush with some IPA would also work well to get between the legs. Of course, it’s always possible (even likely) that goo has gotten under the IC, in which case your best bet is to remove the IC, clean with IPA, and then reinstall.
 

joshc

Well-known member
Isopropyl alcohol should be used to clean the board. Water/soap is fine as long as the board is soaked/rinsed with isopropyl alcohol. A brush may be needed to get rid of dirt in-between IC legs.
 

cheesestraws

Well-known member
Thanks a lot for the detective work! I soaked it in hot water with detergent for some hours. And brushed the board especially around the legs. I will give it another go. Is vinegar a better solvent in this case?

Water and isopropanol dissolve different things easily (being polar vs. non-polar solvents), so using both has a certain amount to recommend it to get rid of general grot. Using vinegar on top is usually unnecessary unless you're trying to remove fairly specific things, mostly battery residues.

If you use both, use the IPA second and make it a thorough washing. IPA both breaks up the surface tension of the water (making it less likely that droplets will get wedged) and helps it evaporate (I think because it forms a lower-boiling azeotrope with water, but I may be wrong—chemistry is a bit of a mystery to me).
 
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