Vintage Computing Pt. 2 - Trying Things Out

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 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!

Vintage Computing Pt. 1

Last year, I came into a bunch of old computer gear from the 1980s.  The inventory is:

IBM PC XT (5150): The one that started it all. This machine sports an Intel 8088 CPU running at 4.77MHz, no coprocessor, dual 5.25” floppy drives and a very lightweight power supply. This particular unit is outfitted with a Quadram board that adds memory, Real Time Clock with battery backup, and expansion ports. This unit has an IBM CGA card and a 1200 baud modem card.

IBM XT/286 (5162): This is an AT class workstation, in spite of its name. It sports a 6 MHz 286 processor, with zero-wait-state RAM that actually makes it faster than its more expensive cousin, the IBM PC AT (5170). No math coprocessor in its socket. This one sports a Hercules GB200 CGA card, which is absolutely diminutive compared to the ‘traditional’ IBM cards. The 5162, being newer than the more expensive and powerful 5170, actually uses SIMMs for memory.

IBM PC AT (5170): This is a original AT class workstation, sporting an 8 MHz 286 CPU. Again, no math coprocessor in this one. It sports an traditional IBM CGA card, along with a memory expansion board to bring the system up to 640K.

Epson Equity 1+: This is a late model 8088 based workstation, much smaller than the IBM workstations and more polished looking. It runs at either 4.77MHz or 10 MHz. It sports 640K of memory, and a Paradise Basic EGA card that can function in multiple modes. This unit had a lot of rust on one side of the case, leaving small chunks to be cleaned out of all the tight spaces around the motherboard.  All of the configuration is performed through DIP switches, similar to the IBM 5150, but these are presented right at the front of the workstation, behind a small access hatch.

Epson Equity II+: This is an Epson 286 class machine, running at 8 or 12 MHz. It sports 640K of RAM, an Epson graphics card, and no DIP switches; all functions are contained handled by the BIOS configuration.

Also found were an IBM 5151 monochrome green-phosphor monitor - slightly burned in, an IBM 5153 CGA monitor in beautiful working shape, and an Epson monochrome monitor.

I’ll continue this series as I work through the process of getting one or more of these grand old machines up and running again.