Macintosh IIci strange power on behaivor

nubus_bagel

New Tinkerer
Nov 19, 2024
2
0
1
DFW, Texas
So, I recapped and cleaned up my IIci a while back now, probably just under a year ago now. It's largely worked fine since, but there have been some strange things it has done, with one of them being an inconsistent power on. If you plug it in after sitting around a minute or longer, it'll automatically power on after about 5-15 seconds. The time isn't consistent, and trying to use the power button does nothing before it boots. After it's plugged in, if it sits off for a while (more than a day, typically), and you use the ADB keyboard to power it on, it behaves similarly, taking a few seconds to react. I believe the rear button doesn't have that issue, but I rarely use it, so I haven't tested it that way lately. Is there anything I should check, or is this actually more or less normal and just not really brought up because of it? Thanks!
 

jmacz

Tinkerer
Mar 21, 2025
46
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18
Certainly not normal… but very common. Leaking capacitors C10 through C13 cause damage to the IIci’s soft power circuit by damaging nearby traces and chips UB13, UD13, UE13. Even if you have recapped those, there could be remaining damage to the traces/chips, or there could also be cap juice remaining under those three chips causing power on issues. Otherwise it could also be your PSU if you haven’t recapped it. If you search for IIci and soft power both on this board and on the internet, you should be able to get ideas on what to look at. Very fixable but you will have to do some debugging.
 
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speakers

Tinkerer
Nov 5, 2021
140
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San Jose, CA
peak-weber.net
Yep. In my case, a similar problem showed up after recapping and persisted after replacement of UE13. Removal of caps C10..C13 again, more cleaning with IPA and application of additional solder mask did the trick though. There's a collection of RC timer circuits sensitve to lingering cap juice leakage.
 
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nubus_bagel

New Tinkerer
Nov 19, 2024
2
0
1
DFW, Texas
Alright, cool! This one has the GE power supply, which seems to kinda just keep working. I opened it when I got it and saw no leaking caps, so while I don't doubt they're worn, the voltage rails are stable, and I think it's okay.

The next time it's acting up badly, I'll take it apart and clean it up, check the ICs, make sure the traces are intact and protected, etc, and report back if it works right after that :)


Thank you!
 
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eric

Administrator
Staff member
Sep 2, 2021
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This got me once but these power buttons can be twisted to a position of consonantly pushed for allowing restarts after power outages. It probably doesn't explain this exact behavior but worth looking and twisting the power button to make sure it's actually "out" or "off" and not being pushed all the time.