DeltaDon
Veteran Member
Yesterday was one of those one step forward, two steps back days. I'm working on a 4 slot S-100 XOR Z80 computer I bought some time ago. The power supply for the twin 1/2 height 8" drives went out and over powered the drives. Bad, but new parts on order. So started on the issue of no serial port communications to my terminal. Found the serial ports wired wrong and fixed that. Yeah! Got a monitor prompt sign on with just the CPU board and one RAM board. Yeah! Started to test various other RAM boards, but kept popping the AC ground fault circuit for the shop. Yes, I turned it off, but not unplugged. So lazy, yes, but a good thing, I guess, for finding a problem before it got worse. I looked for loose wires, dropped hardware etc. Nope. Then realized it happened only when plugging the boards into the back plane with the power switch in the OFF position. Umm? I pressed on the S-100 back plane board without any cards plugged on and "pop" goes the GFI. Reset the GFI and pulled the plug for the computer. I looked under the cage using a strong light and noticed that the 115VAC lines for the main power supply run from the back of case, where the floppy drive power supply resides up to the case front where the main 8 & +/- 16 volt power supply is, by going UNDER the card cage! Yikes. So today I will unscrew a dozen or two screws, remove the cage assembly, and hope to find the chaffed wire(s) and figure out a better path so this doesn't happen again. One very good reason for GFI's!
Update, I forgot to add that during testing one RAM board lit up with flames as a tantalum cap let all the magic smoke out. One more thing to repair.
Update, I forgot to add that during testing one RAM board lit up with flames as a tantalum cap let all the magic smoke out. One more thing to repair.
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