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Mac IIci rebooting every 5 seconds

reallyrandy

Well-known member
I have a Mac IIci that was having sound issues (really quiet, could hardly hear it) so I recapped it last night (while watching Mac84's live cast). Today I put it back together with only four 1 MB chips in bank A and left out the cache card and battery and left the top off the case.
I hooked it up to a 13" RGB Apple monitor drawing power from the wall (not from the IIci) and it chimed and booted perfectly. I tested the sound and it worked fine.
After about 30 minutes, it started rebooting over and over every 5 seconds or so. I unplugged it and re-plugged it in and hit the start button and it did the same thing. I have not recapped the PSU yet but it was fine a few weeks ago.
Any ideas what I should be checking?
 

reallyrandy

Well-known member
I let it sit for 10 minutes and it started up fine, this time after about 5 minutes it started rebooting over and over.
 

Johnnya101

Well-known member
Sounds like bad caps to me. I'd guess the power supply ones are on their way out, judging by the fact that letting it rest "charged them up" and got it going.
 

rikerjoe

Active member
I have a Mac IIci that was having sound issues (really quiet, could hardly hear it) so I recapped it last night (while watching Mac84's live cast). Today I put it back together with only four 1 MB chips in bank A and left out the cache card and battery and left the top off the case.
I hooked it up to a 13" RGB Apple monitor drawing power from the wall (not from the IIci) and it chimed and booted perfectly. I tested the sound and it worked fine.
After about 30 minutes, it started rebooting over and over every 5 seconds or so. I unplugged it and re-plugged it in and hit the start button and it did the same thing. I have not recapped the PSU yet but it was fine a few weeks ago.
Any ideas what I should be checking?
I had the exact same problem with my IIci. My first thought was power supply. However, swapping to a power supply from a Centris 650 yielded the same result. My next thought was the IIci startup circuit on the logic board near the C10, C12, and C13 cap cluster. Sure enough, I found broken traces on both sides of pad 6 of UD13. Adding a bodge wire to ensure pin 6 connected with pin 2 and pin 10 fixed the power cycling problem for me. My recommendation is to check continuity of UD13 and UE13 (I found an earlier broken trace on UE13 pin 1) and hopefully that fixes the problem for you. It is possible that the UD13 and/or UE13 chips are damaged. Modern replacements are available - I used MC74HC132ADR2G from Mouser to replace UE13. Good luck!
 

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jmacz

Well-known member
Thanks for this post @rikerjoe. I just got my hands on a IIci (still has factory caps) and noticed no startup chime. After boot, the sound works but the volume is super low. And then after having it on for about an hour, I shut it off but then on my next attempt to power up, I noticed it would power off within a split second. I currently have to hold the rear power button for the IIci to work - if I let go, power dies. I know it’s not the power supply as I tested using my converted ATX power supply from my Quadra 700 and same problem. The IIci’s power supply works in my Quadra 700 just fine also.

I already have a capacitor kit on the way from console5. I will also examine the chips you mentioned above. Thanks.
 

imactheknife

Well-known member
almost every iici board i worked on had issues with start up circuit and needed more than caps replaced. My last 3 boards were near mint and startup circuit was great with not a lot of cap juice so no need to pull off anything in start up circuit. My rule of thumb, pull off old caps, clean off pads with flux and solder wick, then clean entire board with isopropyl 99% lightly scrubbing everything in the areas of caps etc. let dry. Then add new solder to pads and check traces. Make sure no broken traces etc. recap. If any issues after recap at least you know it isn’t caps or traces in cap area or under A cap.
 

jmacz

Well-known member
Yeah, cleaned the board with ipa as there was some light corrosion on the pins for a few chips near caps. The cleaning removed the buildup and the pins are clean and shiny again. I visually checked all the traces in that section of the board near the power switch and they visually look great. Also checked continuity from the three ICs (all pins) in that area and that’s all good too. Waiting for the caps to arrive to replace and see if it’s any better.
 

jmacz

Well-known member
Replaced all the caps and I'm happy to say the IIci is working like a champ now. Luckily just replacing the caps did the trick. Startup chime is back and the sound volume is great. No more soft power issues also. Going to rebuild the power supply via an ATX board like I did with my Quadra 700. Anyhow, appreciate this thread, it was useful. Thanks.
 
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