In my last post, I have a brief inventory of the five 1980s class workstations I’ve come into. In this post, I’ll outline the issues that are currently occurring with each and what I hope to be able to do with them.
IBM PC XT 5150: This machine powers on and shows a display on the IBM CGA monitor. It displays a memory error, which reveals one or more faulty memory chips on the motherboard. Since the first fault is in Bank 0 - soldered to the board - this goes down my list of repair priority since it’ll require a complete disassembly.
IBM PC XT/286 5162: This machine does not power on: a light whine comes from the power supply when it’s turned on. Very likely a faulty capacitor, so something to explore later.
IBM PC AT 5170: This machine didn’t power on; the power supply fan would spin briefly, and then stop. This indicates either not enough load...or too much. The 5170 power supply is sensitive and will not power on without a load on the 12V line. IBM would include a resistor load for workstations ordered without a hard drive. This unit has the hard drive, so it became likely that a short in the motherboard or an option card is causing the power supply to shut down. I pulled the option cards, and the system powered on. Through elimination, I determined the tantalum capacitor on the CGA card was bad. Snapping it off fixed the problem. From there...the system reported bad memory chips. These are socketed chips...so an easier repair later.
Epson Equity II+: This machine blew the power supply fuse; even when not connected to the motherboard. The power supply is faulty somewhere; swapping the fuse and thermistors didn’t resolve it.
Epson Equity I+: This machine powered up and tries to boot with no errors; it just wants a floppy disk to boot off of!
I made the decision to focus on the most functional machines: the IBM 5170 and the Epson Equity I+. These two represent some great CPUs; and since I have an Epson monitor and two IBM monitors, it all lines up rather nicely. More to come on each!