My most recent project has been too repair a large lot of Tandy 2000 computers. A friend of mine has been collecting these machines for several years and had parts from nine different machines...
We made an agreement that I would work on repairing these machines and we would split the working computers coming out of the repairs but before discussing the repair let's review a bit of history about this machine. These machines were designed and built by Tandy in 1984. They run MS-DOS but they are not compatible with the IBM PC like a Compaq computer from that time period. Tandy had been successful in the computer business since the beginning of the Home Computer era and compatibility had not been a major concern up till that point so they planned to (and succeeded at) building a more powerful computer. These Tandy machines are unique because they have an 80186 processor and many other differences from IBM PCs and Compatibles. Here's an ad from the time showing Bill Gates touting the benefits of this machine...
I'm interested in this period of MS-DOS compatible machines that are NOT IBM PC compatible because I think this is a fascinating period between the end of the 8-Bit CP/M machines and the rise of the PC compatible.
Now onto the repair, as you will see these machines were in rough shape. It turns out that many of the power supplies are no longer working. I created the following pinout table for the power supply connector going into the motherboard:
Nominal Voltages of Tandy 2000 Power Supply
Pin Voltage
Orange +12 V
Grey 5V
Red 5V
Red 5V
Black Gnd
Black Gnd
White -12 V
Blank
Having the pinout and nominal voltages allowed me to go through and sort out the working power supplies. I think some recapping will be required in the future but for now I do have enough working power supplies to get 3 working computers.
Next, I tested the motherboards. Many of the logic boards were showing no signs of life with a known good power supply. The motherboards have 128K RAM soldered on board (4164 DRAMs), and there was a 128K RAM daughtercard that plugged in on the main board itself. I went through and separated these and tested and got a known good 128K RAM board and cycled through the motherboards, reseating and swapping chips that were socketed and eventually getting about half of the boards working but without doing any board level repair.
The lot also included expansion cards for High Resolution Color Graphics. These boards require 256K RAM on the motherboard, and they were needed because the only working monitors we had for this lot were the CM-1 Color Monitor. A couple of the Graphics boards had corrupt video in the color modes, so those were set aside.
The lot also included memory expansion cards that can hold either 128K or 256K on the board. In the base configuration these machines could have up to 512K total, although later modifications could take them higher. Thankfully the RAM chips are socketed on these boards, so I was able to take all the RAM off and cycle the 4164 DRAMs through my RAM tester. After this there was enough working RAM expansion boards to bring the working computers up to 512K.
Next up for repair was the keyboards. I had one working keyboard which had gotten damaged and had a couple of the keycaps broken off it turns out that was just mechanical damage and I was able to re-assemble and glue plastic parts back together. The next repairs required me to take the keyboards apart. One of the symptoms I noticed was that the lights on the Shift and Num Lock keys would come on, indicating that the keyboard had power but then none of the keypresses would work (indicating maybe a bad matrix). Other keyboards had no power on them at all (which may indicate a bad cable). I moved the cables around and I was able to get 3 more working keyboards out of the lot. If needed, the cables can be transplanted into a Tandy 1000 keyboard, but those are getting hard to find, too.
The next order of business was the Floppy Disk drives. The non-hard drive machines had two drives each and surprisingly most of the drives were in good working order. I only had to swap around a couple of the drives and I was able to clean them with a normal floppy cleaning disk. I didn't need to take them apart and lubricate them, although I should. I was able to prove that both the A and B drives were working by using the disk duplication program called compdupe to create copies of the MS-DOS boot disk. This machine can be difficult to create disks for because it's a Double Sided / Quad Density drive that can hold 720K. It works with normal DS/DD media, which I have plenty of, but I still haven't found a way to create disk images, although I understand there are instructions online.
So, this wraps up the repairs, at least for now. My friend and I split up the machines and we are both very happy to have Tandy 2000s in our collection, here's mine...
There's still a bit of extra material coming out of the repair, hopefully enough to make another working machine. This material been offered to another Vintage Computer collector so perhaps the repair project will continue. In the future, I have a couple of upgrades I'd like to do on the Tandy 2000s. I'd like to figure out how to get the Hard Drive working again on the Hard Drive machine or get it working with an MFM Emulator. I'd also like to see if I can replace one of the physical floppy drives with a Go-Tek. This would make it much easier to work with the odd floppy format as there is quite abit of software avaliable for the machine online. But for now I'm glad to have the project completed and move on to to the next Vintage Computer project.
Do you have memories of the Tandy 2000? If so please feel free to reach out in the comments or send me an email, my address is posted in my Blogger profile.
