Logic Board reworking: A Tale of Two IIcx

[Addicted]

I got back to the IIcx's last week. Good news, I think, is that after they sad-chime, their modem ports do echo serial data back (9600 8N1). So either the serial controllers power-up in a loopback mode, or the ROM diagnostic is a real thing and is running.

Bad news, not too bad really, is that I misunderstood what application to run on the remote (host) debugger Mac. What I have is an app that Apple meant to run on the machine being debugged. I need to go back to the books and find the chapter on remote serial boot debug and determine what I need, then go find it on the net.

Once I get one of these systems up, I will have a small amount of wisdom to return to the community. Parts list for recapping a IIcx/ci PSU. A 3D print for the plastic clip that stabilizes the PSU output plug. Info on how to use this debug tool I seek. The Bomarc schematic nit I mentioned above.

And since the fan bracket is deteriorating on one of my IIcx PSUs, I may create a 3D print to replace it, and I'll include that here.

 

[Addicted]

The first IIcx has been checked out by AppleCAT. AppleCAT is finding an issue with SIMM Bank A, and the door remains open for SIMM Bank B - the tests end after the Bank A issue.

I have swapped the 4x4MB SIMMs in bank A out for 4x256KB SIMMs that I had on hand, but AppleCAT still fails Bank A. The 256KB SIMMs are not suspect but, I should verify them by other methods by other means to rule out two sets of bad SIMMs. Old hardware.. it can happen.

I did replace all the SIMM address bus multiplexors due to heavy corrosion. They were replaced with the PSU on/off NANDs, and the PSU wouldn't remain on prior to that. A bad solder joint, lifted pad, broken trace.. all possible.

I've probed the address multiplexors outputs to the resistor packs, and stopped there as the resistors and everything 'beyond' (CPU's perspective) appeared to be free from any corrosion. I do have a set of replacement resistor packs on hand, but my understanding is that they are a very simple passive part that is unlikely to fault. I will undertake the probing from the resistor packs all the way to the SIMM sockets next. Then, I'll check the multiplexor traces to the CPU, and the data lines for each SIMM socket to the CPU. <sigh> And yes, there are some traces between the multiplexors and GLU that might be involved. Looking like hundred(s) of traces to check, and a single break on a single one of them would explain everything. Even lint under a SIMM socket might be the cause.

No one said restoration would be easy

Another mystery remains: the system doesn't even get to the sad chimes unless I have a video card in a NuBus slot. Not focusing on that. One hurdle at a time.

 

[Addicted]

Summary

Macintosh IIcx #2 booted System 7.5 from internal HDD and from floppy today.

It displayed the UI in 256 colors over the RasterOps NuBus card and used MacWeb, Network Time, and MacTCP Ping to access the Internet via a NuBus 10Base-T Ethernet card. 16MB DRAM in Bank A. ADB power-on and OS soft power-off are working. Accessed an external Zip drive. No overclocking; stock 16MHz. It was solid and stable for the hour I was using it, and I may leave it running Speedometer or something overnight.

So:

• CPU, NuBus, Modem Port, ADB, Clock/PRAM, ROMs, PSU and on/off logic, SIMM Bank A, SCSI, speaker, front panel LEDs.
• FPU, Printer port, Sound in, Sound Out, External Floppy. (Test these later)
• SIMM Bank B

Details

Re-lifted and re-seated the six 74F258 RAM multiplexors. Some had dubious solder (my fault). Then, literally two hours of just really dousing the upper face of the logic board with 99% IPA and brushing, brushing, brushing. Found a tiny bit of something, thread? dried up old spider leg?, possiby bridging two pins of UG7. Really focused on GLU due to its proximity to big leaky caps (already recapped). Inspected the underside of the logic board for scratches, broken traces, popped-off SMDs, debris. Let the board air dry for a solid hour.

The RasterOps 8L is proving a little tricky; it insists on coming up in 1024x768, but my monitor is detecting 640x480. So things keep landing off-screen. The RasterOps Monitors Extension shows it has four "Extended" modes all 1024x768 or larger, but the RasterOps controls claim I have no RasterOps card capable of pan, zoom, etc. This has three DIPs on the edge that set the resolution; I'll review to see if I have them inverted.

The Apple Macintosh 8•24 NuBus card may not work. Or perhaps I have not discovered the right DIP settings for my VGA adapter, yet. Would the Apple graphics card sync differently than the RasterOps card?

The PSU now behaves even with no NuBus cards installed; Previously, it would not chime without the Apple NuBus display card installed. Something was pulling down #PFW. Never figured that one out.. but now, it can run headless (as a file server, say).

SO GLAD to have one of these systems booting now. I could live without SIMM Bank B, but, I may try to debug that later. I want to just get the monitor resolution figured out and then enjoy this system for a little bit before plunging in again. I'll run MacTest and AppleCAT again in a few days to try and figure out SIMM Bank B and/or the Apple video card.

Next

There is still work to do. Placing SIMMs in Bank B keeps the system from chiming at all. Possibly bad SIMMs (they came with a DOA system) but not sure how a SIMM could stop a sad chime. And for some reason, cards do not sit fully 'down' in the innermost NuBus slot. I'll look to see if I melted any plastic on its plug. But more worrisome, if a card is in that slot and I put the lid on the chassis, the system stops booting. Logic board may be prone to flexing, pushed down by the lid through the too-high card.

Fun things to do after: I have a box of RAM SIPs to fill the empty sockets on the RasterOps card, and maybe that will let it do higher color. The RasterOps ROM may dictate that, though. Worth a shot.

 

[Addicted]

To debug the SIMM Bank B issue, I placed a SIMM into the four slots in turn, power cycling between attempts, hoping to see a clue that might narrow the traces to check. But this experiment returned the IIcx to sad chimes.

I think I may give up on this hobby.

 

[Addicted]

Positive things to share:

Expanding the memory of the RasterOps 8L does not increase the pixel depth. As suspected, that requires replacing the onboard ROM too. But the RAM alone does enable larger virtual screens, panning, and zooming features. It was cool to have a Nubus video card that could 'do' an enormous pannable screen.

 

[falecore]

Did you try 2,3 and 6 for the dip settings on Apple video card.