IIci Soft Power Issues...

[Colleton]

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?

 

[Colleton]

Well, I replaced both UD13 and UB13 as well as painting all of the traces going underneath the chips with UV solder mask. No joy.

I am really lost on this one, no idea how to go forward. I've ohmed between S1 and UE13/UD13 and everything looks good. Still, you can push that switch all day and nothing happens.

 

[funwithaluminum]

The portion of the soft power circuit that interacts with the machine's OS is circled in green in the image below. Essentially, when the machine is on, pin 1 on UB13 (the reset pin on the flip flop) is pulled high via R112. When you select "shut down" in the Finder, Mac OS does its cleanup work, then signals the ASIC UE9 to pull pin 60 low, which pulls pin 1 of UB13 low, too. This results in pin 5 of UB13 going low which, via a series of steps pulls PS On/Off low, turning off the machine.

In your case, the power on circuitry is generally working properly, and the machine is staying on, which suggests that pin 1 of UB13 is never being pulled to ground, and that you have a discontinuity near where I have drawn the red line within the green circle.

I had a similar problem, except the discontinuity was between UB13 and R112. In my case, the machine would turn on properly, but pin 1 of UB13 would just be floating and the machine would immediately turn itself off again.

You mention that you found no problems with the traces: in my case, the damage was actually within a via. If I had one probe on the via, it would show continuity to pin 1 of UB13, and also to pin 60 of UE9. However, there was no continuity between UE9 and UB13 directly: the multimeter probe in the via was bridging the damage. There were other posts on 68kmla indicating problems with the same via, so I think it is a common problem: the via is right under the big axial capacitors, and I think it is attacked by the leaking fluid.

Maybe this will be helpful to you in fixing that last machine.

 

[Colleton]

Awesome, thank you so much! My wife and I are heading out to dinner and a movie (Top Gun) so I can't look at it right now, but I will later this evening.

This schematic is much more readable than the Bomarc one, thanks!

 

[Colleton]

The portion of the soft power circuit that interacts with the machine's OS is circled in green in the image below. Essentially, when the machine is on, pin 1 on UB13 (the reset pin on the flip flop) is pulled high via R112. When you select "shut down" in the Finder, Mac OS does its cleanup work, then signals the ASIC UE9 to pull pin 60 low, which pulls pin 1 of UB13 low, too. This results in pin 5 of UB13 going low which, via a series of steps pulls PS On/Off low, turning off the machine.

In your case, the power on circuitry is generally working properly, and the machine is staying on, which suggests that pin 1 of UB13 is never being pulled to ground, and that you have a discontinuity near where I have drawn the red line within the green circle.

I had a similar problem, except the discontinuity was between UB13 and R112. In my case, the machine would turn on properly, but pin 1 of UB13 would just be floating and the machine would immediately turn itself off again.

You mention that you found no problems with the traces: in my case, the damage was actually within a via. If I had one probe on the via, it would show continuity to pin 1 of UB13, and also to pin 60 of UE9. However, there was no continuity between UE9 and UB13 directly: the multimeter probe in the via was bridging the damage. There were other posts on 68kmla indicating problems with the same via, so I think it is a common problem: the via is right under the big axial capacitors, and I think it is attacked by the leaking fluid.

Maybe this will be helpful to you in fixing that last machine.

View attachment 5329

Thanks for the great info! I had no idea how the system shut itself down. I spent a couple of hours last night and then a few more today verifying what I had measured last night.

I have continuity from UB13 pin 1 to UE9 pin 60 measuring directly from pin to pin on the two chips. That tells me that the via you mentioned is good, correct? At any rate, I've inspected the via under magnification and ohmed it and everything looks good. As a last ditch effort I did clean the via up with flux and braid and used fresh solder to ensure good connectivity on each side of the board. No change. I have good continuity from +5vdc through R112 to UB13 pin 1 as well.

I have ohmed from SW1 all the way to J14 pin 9, going from component to component along the way. Everything measures correctly for both connectivity and resistance. Both the continuous and switched 5vdc lines ohm good back to J14. I've even tried a different PSU (again) with no joy.

I'm missing something, but have no idea what. I've decided to build an extension cable for the PSU so that I can make measurements with power applied. Should have that soon, but don't think I'll have the time to work on it again for a few weeks.

Thanks for your help!