IIsi death chime after home circuit breaker trips

[JC8080]

I had my IIsi up and running this morning. I just finished recapping the logic board and PSU yesterday, and everything was working great. Up until this point I have successfully booted it 10 times or so. This morning as it was running, a breaker in my home tripped and took out power to the machine. This particular breaker in our apartment has a tendency to trip for no reason, so I think the trip was probably not caused by the computer. Looking at my power strip, I thought it had a surge protector built in, but I don't believe it does.

After that, when I turn it on I get the startup chime, followed immediately by the death chime. There is no video activity, no HD activity. I removed the NUBUS video card and RAM SIMMs and there was no change - still just the death chime.

Edit: after sitting for a few minutes I tried again, using the internal video rather than the NUBUS card. The machine powered up, but there were evenly spaced horizontal lines on the grey happy-mac screen. It moved on to the Mac OS splash screen, and it looked a bit off, there were some odd artifacts. By the time it loaded the desktop background and got to the "you might not have shut down correctly" screen everything looked fine, though I didn't have a mouse hooked up so I couldn't get past that screen.

I shut turned it off and back on and I get the death chime again, I've tried about 20 times with no change.

Any thoughts?

 

[JC8080]

I 2x checked, and my power strip does say it has surge protection

 

[robin-fo]

Your issue could be RAM related. In your position, I would check all the signals of the onboard RAM and bus buffers using a scope.

Do you have an ATX power supply you could rewire to be sure there is or was no PSU-related issue?

 

[JC8080]

Your issue could be RAM related. In your position, I would check all the signals of the onboard RAM and bus buffers using a scope.

Do you have an ATX power supply you could rewire to be sure there is or was no PSU-related issue?

I do have a scope that someone loaned me, unfortunately I don't know how to use it. On the upside I am able to replace the RAM chips if it gets to that. I have a second IIsi PSU that I recapped and which did function yesterday in this machine, the machine shows the same behavior with either PSU.

I'm wondering about the vertical stripes on the happy Mac screen the one time it did start up post-failure. Since the IIsi uses part of the on-board 1mb RAM for video RAM, would those evenly spaced stripes fit with the idea of one (or more) RAM chips being bad?

It's also very possible this failure had nothing to do with the breaker tripping, I bought this machine non-working, so there may have been other failures (or near-failures) on the board other than the leaking caps.

 

[imactheknife]

Could be cap juice has caused issues with onboard ram and vram. Have had to change out lots of those on many iisi boards.

 

[JC8080]

Could be cap juice has caused issues with onboard ram and vram. Have had to change out lots of those on many iisi boards.

Were the actual chips damaged, or did you just need to remove and re-solder?

 

[imactheknife]

The legs had corroded off on them, or pads / traces was damaged. Iisi boards can be nasty

 

[JC8080]

This is a copy/paste of my message in another thread (https://68kmla.org/bb/index.php?thr...ic-chime-sound-what-does-it-mean.31492/page-5), I'm putting it here in case someone stumbles across this thread in a search.

Death chime fixed! Hopefully this info helps other people with the same issue. Steps taken:

Re-flow all the onboard RAM, the legs of the chips closest to the leaking caps showed corrosion. This did not fix the problem, but these corroded legs might have been a contributing factor.

Next, when I was checking over the board with my microscope, I found a couple legs on the CPU were loose. I re-flowed all the grungy looking pins and checked for continuity from the top of the leg to the pad, to ensure my reflow job was solid. I did not try starting the machine at this point.

I also noticed some loose legs on some of the ALS245 chips (UE5, UF5, UG5, and UH5), I removed all four chips, checked for broken traces around/underneath (there were none), and re-soldered. At this point I meticulously checked continuity from every pin of each ALS245 to it's destination (other ALS245s, onboard RAM, RAM SIMM sockets, ROM SIMM socket, CPU, UJ3 chip) and confirmed all were good.

At that point I booted the machine - the death chime was gone, just the normal chime remained, and it seems to be functioning well. Audio works, keyboard/mouse work, SCSI works, video works, NuBus video card works. I still need to go in and poke at the pins of the other grungy looking chips on the board to see if any are about to come loose, and maybe re-flow any that look suspect. But at the moment everything is working!

Thanks to @imactheknife and @Phipli for the guidance.

 

[imactheknife]

Sweet, glad we could help in some way! Enjoy the old mac

 

[JC8080]

Well I spoke too soon, shortly after that May 2nd post the machine began the death chime again and would not boot. I put it on the back burner since I did not have time to work on it. I decided to work on it some more recently, I replaced the ALS245 chips with new chips from DigiKey, there is no change in behavior. Here is what I have done so far:

• Re-capped the logic board
• Re-soldered the CPU pins near a leaking cap, since a couple were loose, and checked continuity of all CPU traces in the affected area
• Replaced the onboard RAM with known-good chips (taken from four matching 2-chip 256kb SIMMs)
• Replaced the ALS245s, and checked continuity on all pins to their end points, except I overlooked tracing them to the onboard ROMs. I did check continuity to the ROM SIMM slot.

The death chime happens very quickly after the boot chime, less than a second. I have removed the RAM SIMMs and the video card - I am testing with only the board, power supply, and speaker. The power supply is re-capped, and I also have also tried a second re-capped PSU.

I am hoping someone can point me in the right direction for some troubleshooting. I have a scope I am learning to use, so I am able to check signals. I do not mind pulling chips and re-soldering, but I want to make sure I am putting my time into chips that are likely to cause this issue.