[Solved] Mac iici boots to gray screen

[point5]

Hi all, new to the site, what a great resource! I'm working on a iici, that is in pretty good shape, no battery leakage, just the typical cap leakage. It starts up, chimes and produces a gray screen but no mouse and nothing more. I have recapped it, checked for broken traces but didn't spot any, and reflowed some of the crusty looking solder on the chips that were close to the replaced caps. The only chip with a heat issue is the CPU. After running it for about 5 minutes it is hot to the touch. All other chips remain room temp. I got good tested ram in bank A. Was thinking of breaking out the O-scope to check the address and data lines next, but thought I'd post here to see if anyone knows of some common issues I should check. Also I have popped in a rominator II (and pulled the jumper) to see if the on board rooms might have an issue, but got the same results.

 

[point5]

Posting an update, so far no luck. I read about a utility called appleCat which lets you hook a working Mac to a problem Mac via a serial cable connected to the modem ports of each unit. I was able to build a loopback plug for the printer port and lucked out and acquired the SCSI loopback card so I have the hardware required for testing. The only pain part was the software itself, the only version I could find online for the iici (yes there is a versioned app for each model!!) was in French, so I had to use an iPhone to translate the messages on screen. I was able to run the app and get a connection between the 2 units. The app is saying there is a problem with the ram, but I know the ram is good as it works fine in a different working Mac that also uses this type and speed of SIMM. This led me to suspect something was wrong with either a chip or a trace. I have checked connectivity from the ram sockets to the the MDU chip and from the sockets to the 4 74f245 chips and all ping out fine, per the Bombard schematics. The board itself is in really decent looking condition around the sockets, the MDU, and the entire lower half really. The only crusty areas are towards the top where all the old caps had leaked. Given that it powers up and chimes, and that I was able to establish communications between the 2 Macs, Id say the majority of this board is working. At this point short of pulling chips from a donor board at random, I am not sure what type of testing to try next. Any one have any ideas?

 

[Kai Robinson]

Hmm - have you got the IIci schematics to work with, first of all?

 

[point5]

I am using the Bomarc schematics. I found a pdf online and re-stiched the half pages back together in photoshop so I can look at them as flattened full pages.

 

[ClassicHasClass]

How is the RAM configured in the SIMM slots? Are they all the same specification? Do you have them in matching groups of four?

 

[point5]

I have tried several things. 4 - 1mb sticks of 70ns in bank A - nothing in bank B, 4 - 4mb sticks of 80ns in bank A nothing in bank B, and 4 - 1mb sticks of 70 in Bank A with 4 - 4mb sticks 80ns in bank B. All scenarios give the same result. Both sets of simms work fine in a performa 600 as a group of 4, so I know they are good. I suspect something is up past the sockets. when the machine boots, I only get the start up chime. when the ram test is run from the appleCat program, after confirming the size of the sticks, I get the bad ram chime (sad Mac sound). so the utility cannot check the ram successfully but it seems the iici can. Truly a mystery.

 

[point5]

Also just wanted to say thanks to everyone for any help given. Sincerely appreciated.

 

[Kai Robinson]

Then you may find the Apple original schematic helpful, too

 

[point5]

Thanks Kai, I was beginning to think the apple version was lost to the ages! heh. Hopefully I can spot something new with this version.

And incase anyone in the future might find it helpful at all, I will add the pdf I have been using here as well.

 

[point5]

Update #3 for those following along...
Using the schematics provided by Kai (many thanks), I was able to tone out all of the chips in the area around the power button (ADB, swim, via, scsi, etc.) After confirming connectivity, I went on a hunt for more information about the boot up process and ran across this page
https://macgui.com/news/article.php?t=496 (have to sign up to see the whole article, but worth it!)
which describes the boot up process and the rom functions involved, including the audio and visual clues given on screen that you have reached certain milestones, things like the different chimes, when black screen goes to grey, and when the cursor appears. Having that info allowed me to surmise I had an issue with something to do with the initialization of the cursor sprite. My guess was that I had a bad ADB chip (UA13 on the iici board). Swapping that out from a donor board was not fun as I am not heavily experienced with a hot air rework station. I managed to get the old chip off, but must have loosened some pads because I lost a few while cleaning them. fortunately only one of the missing pads was vital and that one was connected to the pin next to it, so a bodge from pin 2 to pin 3 and I was good to go. And Success! The machine booted successfully for the first time since I acquired it. That said there is still one problem, I can't seem to shut it off with the button on the back. So, after choosing shut down from the menu, and seeing the black screen with the message telling me it is safe to shut down, pressing the button does nothing. This is new. Prior to this when I could not get past the grey screen pressing the button always cut the power. If any of you has seen this before, I'd appreciate your input. Until then I'll be searching all the usual forums for a clue.

Again a big thanks to all of you who helped get me this far.

 

[Kai Robinson]

Sounds like you need to redo the soft power/startup circuit, usually a recap, but check all the traces around and under the 74LS chips. Also the logic there can just die, so worth replacing them while you're at it.

 

[point5]

So, after some quick googling , I went down a rabbit hole and replaced the HC132 at UD13. But of course that was not it. Next I took voltage readings at pin 3 of UD13 while running before and after pushing the power button, it flopped fine. So I traced the +5v from there through all the diodes till I got to Q3. It was the collector leg of Q3. It was not touching the pad, though it sure looked like it was. Grounding it while the unit was running did nothing when I touched the pad, but touching the leg shut the machine down proper. Just a quick blob of solder fixed that right up. And I have a fully functional Iici. Hooray! Once again thanks to all who responded, the suggestions you provided nudged me in the right direction and allowed me narrow down the possibilities and come to the right conclusions.

 

[point5]

One last unrelated item on this, one of the clips that hold the ram in place was broken and the last chip in bank B could not be kept in place. I created and 3D printed a clip to hold the chip in place. If you might find it useful, it is freely available on thingaverse. https://www.thingiverse.com/thing:6558885