I was an electronics technician in the Air Force back in the day, but it had been a long time since I'd done any electronics repair work when I became interested in retro computers a few years ago and began buying them to enjoy. I started with Ataris because that's what I had back in the 80's, and then switched over to 68K Macs simply because they are more complicated and more fun to tinker with. I had never owned a Mac until I bought that 1st 68K machine (it was an SE/30). I've watched a lot of videos by Bruce Rayne, Mac84, HoM, Adrian Black and others, so thanks for the help from all those whose videos I've watched.
I have 4 IIci computers (no, I don't have a problem), 2 of which work perfectly and 2 have soft power issues. Of the 2 that have issues I've recently repaired one of them so really I have 3 that work perfectly now. The remaining machine is still being recalcitrant.
#1: This machine came to me in pretty poor condition. Two of the SIMM slots on the logic board were broken, and the surface mount electrolytic caps had leaked badly. I recapped the board and replaced the broken SIMM slots (fun times with my Hakko de-soldering gun). After all that it would chime and boot, but the computer was powering on as soon as it was plugged in. I replaced all of the parts in the power-on circuitry, but the problem ended up being a broken trace right at the pad of pin 14 on UE13. This is the Vcc for the chip, so UE13 was not being energized normally. Used a bit of wire to repair the break and voila, the computer works properly. Incidentally, while troubleshooting this I noticed that the Bomarc schematics show the +5vdc going to Q4 (as well as pin 14 of UE13, although it isn't shown) as coming from pins 2, 3 and 4 of the PSU when it is actually coming from pin 10, which I think is the low current "always on" +5vdc line.
#2: This computer has had the usual recap and clean-up and it works perfectly, with one exception - it won't shut down via software. When I try to shut it down I get the "It is now safe to turn off your Macintosh" screen. Pressing the power switch on the logic board does nothing once you're at this screen. I've replaced all of the power-on circuitry components (IIRC) and ohmed all of the relevant traces that I can find in the schematic. It isn't the PSU as I've tried a known good PSU in this machine with the same result. I have no real idea where to go from here. It seems to me that the "Signal Line" going to pin 9 of the PSU is being latched on so the PSU can never be shut down. So maybe it could be UB13 or it's associated traces causing the problem? Any thoughts or ideas? Has anyone else run into this before?
I have 4 IIci computers (no, I don't have a problem), 2 of which work perfectly and 2 have soft power issues. Of the 2 that have issues I've recently repaired one of them so really I have 3 that work perfectly now. The remaining machine is still being recalcitrant.
#1: This machine came to me in pretty poor condition. Two of the SIMM slots on the logic board were broken, and the surface mount electrolytic caps had leaked badly. I recapped the board and replaced the broken SIMM slots (fun times with my Hakko de-soldering gun). After all that it would chime and boot, but the computer was powering on as soon as it was plugged in. I replaced all of the parts in the power-on circuitry, but the problem ended up being a broken trace right at the pad of pin 14 on UE13. This is the Vcc for the chip, so UE13 was not being energized normally. Used a bit of wire to repair the break and voila, the computer works properly. Incidentally, while troubleshooting this I noticed that the Bomarc schematics show the +5vdc going to Q4 (as well as pin 14 of UE13, although it isn't shown) as coming from pins 2, 3 and 4 of the PSU when it is actually coming from pin 10, which I think is the low current "always on" +5vdc line.
#2: This computer has had the usual recap and clean-up and it works perfectly, with one exception - it won't shut down via software. When I try to shut it down I get the "It is now safe to turn off your Macintosh" screen. Pressing the power switch on the logic board does nothing once you're at this screen. I've replaced all of the power-on circuitry components (IIRC) and ohmed all of the relevant traces that I can find in the schematic. It isn't the PSU as I've tried a known good PSU in this machine with the same result. I have no real idea where to go from here. It seems to me that the "Signal Line" going to pin 9 of the PSU is being latched on so the PSU can never be shut down. So maybe it could be UB13 or it's associated traces causing the problem? Any thoughts or ideas? Has anyone else run into this before?
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