Sick Mac IIci Board

[ajacocks]

I've got a Mac IIci board that has had a couple of problems, over the last year:

1) the board is mute

2) the board powers off, after approximately 30 minutes of use

I fixed the first problem by replacing all the capacitors in the sound section of the board, this weekend. Thank much to trag, for supplying the caps!

The second problem, however, remains. I've replaced every capacitor (PTH and SMT) on the board, to no avail. I've also replaced the power supply with a known-good unit. It seems to me that I have narrowed the problem down to only one possibility, though it's an unappetizing one: one of the SMT ICs on the board is heat-sensitive.

The problem is that it's really beyond me to replace a multi-hundred pin SMT IC, and, even if I could, the cost of the parts, when available, is prohibitive.

Does anyone have a last suggestions, before I consign this board, that I have worked so hard on, to the scrap/spare-parts pile?

Thanks!

- Alex

 

[trag]

The power-on circuitry is fairly simple and does not involve any 100 pin chips. Probably a few of those tiny surface mount transistors.

There is a schematic of the circuit around somewhere, but I have no memory of where. With a little luck, someone else will come along and post a link. You may wish to start a new thread, "Schematic for IIci Power-on Circuit?"

I would also check that you have good continuity between the caps in the power-on region and the board pads.

 

[Charlieman]

Please can you define "the board is mute". No startup sound? No boings when operating?

 

[Unknown_K]

He said he fixed the sound issue already.

Look for crud around chips close to the capacitors you replaced, something could be shorting out some pins?

 

[ajacocks]

I should have mentioned that I cleaned the crud off of the board, when I replaced the caps. Continuity seems to be OK, but I don't, in all cases, know where to verify it from. I did personally scrutinize the quality of the solder joints, and had someone else double-check me.

I was planning to strip the board, and run it through the dishwasher, to try to get out any leftover crud that might be under an IC, or invisible to me.

As far as a schematic goes, I'm not sure that I would have the expertise to verify functionality, using one. I can, and would, definitely try, given some suggestions, though.

Thanks!

- Alex

 

[zuiko21]

The schematic of the IIci start-up circuit, from Gamba's site:

Unlike the II and IIx, it doesn't seem to have a thermal sensor anywhere, which could cause the symptoms you mention... anyway, it's a pretty simple circuit to troubleshoot. The ICs are SMT, but 14-pin only :b&w:

You did change all capacitors on the board, right? Particularly C11 and the associated R33 resistor -- if it looses its charge somehow, computer will shutdown sooner or later! Check the area around these and, just in case, the solder joints of the power connector on the board.

 

[ajacocks]

Thanks, zuiko21!

Yes, I did change every capacitor on the board. I didn't change any resistors, though.

The thing that makes me think thermal issue is that, after the 30-minute shutdown, if I try to start the IIci back up, again, it will power on, but then it immediately powers off. If I wait for a while, then everything is back to normal. That really says heat, to me.

The fact that there is no thermal shutdown system does throw me for a loop, but I suppose it must just be some IC that is experiencing heat failure.

Thanks!

- Alex

 

[zuiko21]

Your issues definitely look like heat-related... even if there's no thermal shutdown device.

Just a thought: maybe there's some metallic piece (or solder joint) which dilates on heat and ends up shorting some power lines, forcing shutdown? The problem could reside on the power push-button at the back of the computer...

A somewhat unrelated note: my Dad's 7500 was experiencing some random power-UPs, from a few seconds after shutdown, to hours or even days later, even in the middle of the night -- crazy! I tried everything described here to solve the issue, to no avail -- even the "defibrillation" procedure 8-o

...eventually, I solved the problem by replacing the ADB keyboard -- seems like it shorted the power-on signal randomly xx(

 

[joe4227@sympatico.ca]

I have a MacIIci with similar symptoms, which then failed to boot. Am in the process of re-capping now.

BTW, just a thought - did you replace the Battery with a new one, and reset the PRAM?

If the Battery is bad, it will drain the power-on circuit, and shut down.

 

[ajacocks]

Thanks for the suggestions, but I have a bunch of ADB keyboards, so unless it's the port on the IIci (possible), I don't think that it is that. And, yes, I've replaced the PROM battery.

In the meantime, I seem to have acquired an Apple TechStep diagnostic unit. If I can hunt down the CPU module for the IIci, I'll try that, and see if it gives me any clues.

The suggestion about a possibly bad solder joint is an interesting one; I'll start trying to check all the joints that I can see.

Thanks!

- Alex