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Not to over-post.. but what happens when I wire up the internal SCSI port for control line monitoring? Everything starts working again, instantly. This is very good news, on the one hand. The NCR 53C96 is not dead. My test disk is not dead. OTOH... I may have a 'gremlin' kind of problem...

Ordered a 4MB ROM SIMM from CayMac, which should boot 7.1U3 on a C610 (now Q610: I put in a full 68040) right out of the box. Hopefully, this will allow me to test the Ethernet and modem ports, get a network up on one or the other, and download anything I need to proceed. Still very awkward to...

Studying the NCR 53C96 data sheet, which may give enough basics on SCSI bus transactions to allow me to narrow the possibilities a little. Without tracing (via oscilloscope) the data bus as well as the control lines, though.. I won't get too far. First step is to probe a few pins on the 53C96...

Yes. In tests where I don't want the old Quantum with the bad blocks to be a part, I pull its power but leave the SCSI cable in place. Saves strain on the SCSI cable. My understanding of passive termination is that the Quantum's resistors still do their part, powered by the termination power...

Thanks for the nudge. I finally did my homework. Centronics printer cables use a 36-pin connector. I haven't seen one in decades and never had one of my own, so, forgive my confusion. Although, now I have zero leads on why my MCCS142235 terminator chip was hot to the touch... :unsure: Plan A...

Yes, those are great. I used those when I replaced the NANDs and the FF that first allowed me to reach the Sad Chimes.

After sleeping on it.. I have at least two problems, I think. The recapped PSU changed the behavior of the board. And the board may be tweaking the power fail trace, which may have always been the real reason the PSU seemed to need a recapping. After recapping the second power supply, its logic...

I think I saw the thermal shutdown switch while recapping the PSUs. It's attached to the heat sink for the FETs, inside the supplies. I'll investigate it if I reopen either of them.

So, something appears to be pulling #PFW (power fail warning?) down, which would explain the PSU clicking problem that is my latest setback. Oddly, if I plug a RasterOps Nubus card in, the PSU remains on, and PFW is not pulled down. Odder, if I plug either an Apple Nubus Video Card (630-0400)...

All I learned today is that.. nothing seems broken. So I am barking up the wrong trees. Something is broken. I booted from floppy with nothing on the SCSI bus. The 142235 termination chip remained cool. The regulator that provides it with 2V85 was working to spec, outputting 2.83V. Placing the...

Finished one of the two IIcx PSU recappings. I chose the one for the IIcx that won't stay on, the one that click-click-clicks its relay instead. Putting that PSU back in its IIcx, the system still just rapidly cycles when powered on. That's no surprise; I suspected corroded PSU logic on the...

The PSU parts are due Wednesday (as in 31 Jul). As I plan the rebuild, I was wondering why one, not both of the large 470uF/200 working voltage caps is wrapped both in paper and again in heat shrink? Is this thermal protection? Static discharge protection? Vibration protection?

Post in a nutshell: repairing a Centris 610 I literally found in the trash. It was looking most excellent until I plugged in two VRAM SIMMs... and the SCSI bus died. Which puzzled me. Now, I've found a chip running much too hot. -- -- details -- -- Perhaps the VRAM had nothing to do with it...

Excellent replies, thank you. BTW the Mac IIsi was the first Mac I owned. I loved that machine. I had the Apple FPU+NuBus adapter card. I forget whether my first NuBus card was a video card or the Pro Audio Spectrum 16. Probably the latter. So, IIcx. I spent Saturday afternoon dismantling one...

Recap early! I did not and sadly, my good fortunes did not last. I managed to get the original internal HDD of my dumpster'd Centris spinning and booting again by leaving it powered up all night. I then attached another HDD and an external Jaz 1GB drive, low-level formatted the internal HDD to...

My, I do ramble. What I meant to conclude with, was even with a board that has corrosion like mine, the system can be stable - but I still will risk the rework to replace the leaked caps as a priority. The caps were in the design for a reason, and new caps preserve that design. Getting the...

Well, I did a virtual dumpster dive today. I was out for a walk. It was trash collection day on the block. There was a Centris 610 just lying out on the curb for collection. It looked like it had been exposed to a lot of soot or some other black dust, but was only missing the cosmetic panel for...

I was lucky to land a non-working IIcx on the cheap. It looked better than it really was; the PSU would not stay on but would instead rapidly cycle on and off. After a basic recap, nothing improved. Lifting one of the chips in the PSU on/off support area (under the FDD/HDD caddy) revealed a lot...

Are you certain the battery isn't nearly dead? Removing it and replacing it might allow a really weak battery to build up enough residual charge while it is removed to get the OS running again, but it would then be so very borderline that very shortly, it would no longer be able to repeat the...

Follow-up: I didn't fix my IIcx, and now think the problem is not the logic board. I recapped my IIcx, then replaced UK2, UL2, UM2, D5 - D7, Q2, Q3, as well as the RAM bus multiplexors H1/2/3 - J1/2/3. These chips all showed signs of corrosion on their leads and I was able to inspect the pads...