I have managed to resurrect mine. I had a cap backwards. I works, but it will turn machine on when I plug it in. I can't shut off without unplugging it. I checked to see if power button was turned but its not. Any ideas?
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iisi power supply
- Thread starter imactheknife
- Start date
yeah I did, dont want to unsolder that again lol...what I little pain in the arse that is
@imactheknife did you ever figure out what was going on with your power supply?
I'm cleaning up a IIsi for sale. I have recapped the main board and the power supply (including the daughter card). Prior to recapping both boards, the IIsi would not power up at all.
After recapping, I have both the main board and power supply sitting out of the case on a bench for testing. I plug everything in and it sits nice and quiet. Good. I hit the power button on the keyboard and the IIsi powers up and boots. Great. Run some tests and everything looks perfect. I then choose Shutdown, the system powers down. About 3-4 seconds later, it automatically powers back on by itself and starts booting. Tried a few times and same thing.
The main power button is not set into server mode as again, the motherboard is sitting out of the case.
I then tried by replacing the power supply with a power supply from a IIci. That one works great. No issues shutting down. It stays off. Soft power works, everything is fine. I then swap back to the IIsi power supply, same problem. It won't stay powered down. So this looks to be a PSU issue, not the mainboard.
I then read some other threads on this forum and took a closer look at the daughtercard. The IC on that daughterboard still had gunk on it. So I took that daughterboard out (again), cleaned it all up, removed the IC and cleaned underneath, resoldered the IC onto the board, check connectivity of all pins on the IC, checked connectivity on all the diodes, capacitors, resistors and all looked good. No broken traces. Soldered the daughterboard back in and tried again. Same result. The IIsi won't stay powered down. But everything else including soft power works great.
After playing with this, I left the PSU plugged into the mainboard and power for about 15 minutes. When I came back to test again, it started working. It will stay shut down.
Umm... I don't get it. I've got it sitting completely unplugged to see if I can reproduce the issue in a few hours.
Before I start dismantling that daughterboard again and starting a long process of testing all the resistors, etc, anyone have any suggestions on what else to try?
Again, IIci PSU works fine on this IIsi mainboard so that rules out the mainboard. Soft power works great. Power on works great. Everything is stable. It just won't stay powered down after a cold power on. After getting warm, it seems it does the right thing. And I've checked all the solder joints and traces (there's not that many on this board).
I'm cleaning up a IIsi for sale. I have recapped the main board and the power supply (including the daughter card). Prior to recapping both boards, the IIsi would not power up at all.
After recapping, I have both the main board and power supply sitting out of the case on a bench for testing. I plug everything in and it sits nice and quiet. Good. I hit the power button on the keyboard and the IIsi powers up and boots. Great. Run some tests and everything looks perfect. I then choose Shutdown, the system powers down. About 3-4 seconds later, it automatically powers back on by itself and starts booting. Tried a few times and same thing.
The main power button is not set into server mode as again, the motherboard is sitting out of the case.
I then tried by replacing the power supply with a power supply from a IIci. That one works great. No issues shutting down. It stays off. Soft power works, everything is fine. I then swap back to the IIsi power supply, same problem. It won't stay powered down. So this looks to be a PSU issue, not the mainboard.
I then read some other threads on this forum and took a closer look at the daughtercard. The IC on that daughterboard still had gunk on it. So I took that daughterboard out (again), cleaned it all up, removed the IC and cleaned underneath, resoldered the IC onto the board, check connectivity of all pins on the IC, checked connectivity on all the diodes, capacitors, resistors and all looked good. No broken traces. Soldered the daughterboard back in and tried again. Same result. The IIsi won't stay powered down. But everything else including soft power works great.
After playing with this, I left the PSU plugged into the mainboard and power for about 15 minutes. When I came back to test again, it started working. It will stay shut down.
Umm... I don't get it. I've got it sitting completely unplugged to see if I can reproduce the issue in a few hours.
Before I start dismantling that daughterboard again and starting a long process of testing all the resistors, etc, anyone have any suggestions on what else to try?
Again, IIci PSU works fine on this IIsi mainboard so that rules out the mainboard. Soft power works great. Power on works great. Everything is stable. It just won't stay powered down after a cold power on. After getting warm, it seems it does the right thing. And I've checked all the solder joints and traces (there's not that many on this board).
I've had this issue so many times when working on IIsi machines. It's really really frustrating to track down. The only theories I have that may have an effect are the cleanliness of the PSU and logic board itself.
On one machine, I found that some electrolyte fluid had made its way under the power connector on the logic board, thus decreasing the resistance between the PFW and trickle lines. Removing the connector, cleaning, and replacing seems to have fixed the issue on that board.
In another instance, I had to soak the entire power supply board in IPA. That worked in that second case. Based on what I've seen, swapping the little soft power board has no effect on this "power on" issue. I really do believe it's related to leaked cap juice affecting the 5V trickle and power watchdog.
I hope this helps in your troubleshooting!
On one machine, I found that some electrolyte fluid had made its way under the power connector on the logic board, thus decreasing the resistance between the PFW and trickle lines. Removing the connector, cleaning, and replacing seems to have fixed the issue on that board.
In another instance, I had to soak the entire power supply board in IPA. That worked in that second case. Based on what I've seen, swapping the little soft power board has no effect on this "power on" issue. I really do believe it's related to leaked cap juice affecting the 5V trickle and power watchdog.
I hope this helps in your troubleshooting!
A soaking of the PSU main board in IPA seems to have corrected the issue. I can’t reproduce now and it’s working great. Thanks for that tip @Garrett B ! I had thought I cleaned that main board enough but clearly there was some more gunk under the other components. The daughter board I had soaked but not the main board which I visually inspected after removing all the caps. Clearly wasn’t enough. Thanks again!
Yeah, never did get it working. I bought a working one. I have another one that i Will now soak and try now.
Awesome news! Keep us updated if it decides to start acting up again.
Good luck!
I too have hit this soft power issue.
I picked up a IIsi for which the logic board was mostly fine although needing a recap. The PSU was a disaster, however: trickle supply was OK but nothing else. Cap goo was everywhere. The main HV caps were fine but I replaced the rest. Here's one example of what was there:
Three (1k) resistors on the low voltage side had legs completely eaten away by the electrolyte!
I scraped, scrubbed, cleaned, recapped and re-assembled. All voltages were then fine on the bench. I'd tested the logic board first with an IIci PSU and all was well. But when I installed the IIsi PSU, the IIsi fired up fine -- the soft power refused to work. So .. another case of this issue.
I guess I have to dismantle, check the ON/OFF circuit and clean some more.
jmacz - what exactly was your IPA soaking method for the main PSU board?
I picked up a IIsi for which the logic board was mostly fine although needing a recap. The PSU was a disaster, however: trickle supply was OK but nothing else. Cap goo was everywhere. The main HV caps were fine but I replaced the rest. Here's one example of what was there:
Three (1k) resistors on the low voltage side had legs completely eaten away by the electrolyte!
I scraped, scrubbed, cleaned, recapped and re-assembled. All voltages were then fine on the bench. I'd tested the logic board first with an IIci PSU and all was well. But when I installed the IIsi PSU, the IIsi fired up fine -- the soft power refused to work. So .. another case of this issue.
I guess I have to dismantle, check the ON/OFF circuit and clean some more.
jmacz - what exactly was your IPA soaking method for the main PSU board?
No "method" 
but basically I didn't want to submerge the whole thing so I just put the PSU board into tupperware and then poured in 99% IPA until it just barely covered the board, and left it there for about 20 minutes and then took it out, let the IPA drip off, and then let it air dry.
I usually submerge motherboards but didn't feel comfortable submerging the PSU.
but basically I didn't want to submerge the whole thing so I just put the PSU board into tupperware and then poured in 99% IPA until it just barely covered the board, and left it there for about 20 minutes and then took it out, let the IPA drip off, and then let it air dry.I usually submerge motherboards but didn't feel comfortable submerging the PSU.
Thanks. With a relay and transformers to worry about, I too am thinking about a very shallow, barely-covered bath.
IIsi power supplies are unfortunately some of the most notorious for this kind of thing. I don’t know what it is about the caps in those things.
I had one that where the cap goo all leaked out of the PSU and onto the printer port serial chip below and dissolved its pins. I discovered it during the logic board and PSU recap process. Not pretty. Too bad I love the IIsi so much.
I had one that where the cap goo all leaked out of the PSU and onto the printer port serial chip below and dissolved its pins. I discovered it during the logic board and PSU recap process. Not pretty. Too bad I love the IIsi so much.
Yikes, I'm surprised goo had got to the back end of your machine. Mine had goo fromt the low-voltage side oozing out towards of the front end. Luckily, it hadn't reached the logic board.
I gave the main PSU board a good IPA bath but sadly that didn't help (though it looks much better now). I need to pull out the daughter board (again) and take a look under the regulator chip. I measured too low a voltage at the ON/OFF pin which is probably due to electrolyte under the chip. Thankfully, I invested in a Hakko desoldering gun!!
I got the daughter board out again and took off the regulator chip:
Gag. Loads of goo and solder mask eaten through to a ground trace. That was pulling pin 7 down to about 0.2v and resulting in the regulation always being enabled. Pin7 is pulled up to +5v by a 100k resistor so the electrolyte seemed to provide about 4k to ground! Sounds a lot but it must be possible.
Got it all cleaned up and back together .. and soft-power is working again.
BTW: for anyone using the Bomarc schematic for this board, there are errors and omissions. I noticed:
Gag. Loads of goo and solder mask eaten through to a ground trace. That was pulling pin 7 down to about 0.2v and resulting in the regulation always being enabled. Pin7 is pulled up to +5v by a 100k resistor so the electrolyte seemed to provide about 4k to ground! Sounds a lot but it must be possible.
Got it all cleaned up and back together .. and soft-power is working again.
BTW: for anyone using the Bomarc schematic for this board, there are errors and omissions. I noticed:
- Board pin5 is ground.
- IC pin18 has a 8.2 ohm resistor to ground (not 8200).
- The 100uF cap doesn't appear in the schematic.
So many people give up on these unfortunately, including me lol. Good job
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