Mac IIsi death chime after home curcuit breaker trips

[JeffC]

I just finished recapping my IIsi logic board and PSU yesterday and it was working great. I had powered it up and down at least 10 times, it worked great each time. This morning I had it powered on and a circuit breaker in our apartment tripped. This particular breaker tends to trip occasionally on its own, or sometimes if there is a space heater plugged into the same circuit, but that was not the case today. I think it is likely the IIsi did not cause the breaker to trip, though maybe the 13" CRT pulls more power than I think. Also worth noting, I thought my power strip had a built-in surge protector, but I think it does not.

After I reset the breaker and tried to power up the machine, I get the startup chime, followed immediately by the death chime. Immediately after powering on, the screen is grey for about half a second, then goes dark. There is no attempt to access the HD. I tried multiple times with the same result. I removed the NuBus video card and RAM SIMMs, there was no change in behavior. I let the machine sit for a few minutes then thought I would try with the onboard video. I powered it up and there was no death chime, it progressed to the grey happy Mac screen, but there were evenly spaced vertical lines about 1" apart. It moved on to the MacOS splash screen which looked semi-normal, but had odd artifacts around the edges of text. Then it loaded the desktop background and brought up the "you might have shut down incorrectly" message. It all looked perfectly fine, but I didn't have a mouse connected so I couldn't go any further. After that I have tried to power it up about 20 times, and I get the death chime every time. I think it is unlikely using the onboard video vs NuBus card actually made any difference, I have tried both since then, and I always get the death chime.

Edit: my power strip does say it has a surge protector.

Any suggestions?

 

[JeffC]

Responding to my post in case someone runs across this 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!

 

[JeffC]

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.