Today I came across some early British "valves" at a local hamfest. You don't see too many of those on this side of the pond. The two small tubes are type VR 21, introduced in 1929. The clear tube is a S-130, first introduced in 1935. The final tube is a 4046A (aka CV244).
Picked up a TRS-80 today for free today. A colleague of mine (who had retired several years ago) called me up out of the blue. His wife wanted him to get rid of his old TRS-80, so I took it. Looks like I might have to do some work on it judging from the garbage characters on the screen. Also have two floppy drives, cassette recorder, modem and a few other goodies.
Saw this Altair 8800 at a local fleamarket. Never saw one in the flesh before. A bit priced outside my range, but cool to see nonetheless. There were also a few other goodies here.
Mod 80 Restoration - Been spending the last month or so drafting up replacement circuit boards for the Mod 80 computer. I have a few more to do, before I have a complete set, but I have all the ones I need done. I also need to make up a power supply board and a 1702A EPROM reader/burner circuit. Then I will send those off to be professionally done.
Met Dave Kerr at the Hamfest in Brampton. He gave me a number of old chips for the Mod 80 along with a decent 5V power supply. Among the chips were some more 1702A EPROMS and several dozen 2102A RAM chips, including a great many early MIL gold plated chips. Some were made in 1972. Also got a nice MIL MF8008A CPU chip as well. Among the parts I got there was another custom vector board that was made so that the monitor 80 code located in high memory could be executed automatically upon system reset.
Mod-80 Restoration: Got a hold of a RS232 to current loop converter. This allows me to connect the teletype to my PC. I was successful in both transmitting and receiving data from teletype machine at 300 baud. Now all that remains is to figure out why the print head occasionally doesn't line up correctly. Ordered a full manual with schematics for troubleshooting. Hopefully I can solve the issue.
If not, the tests proved that I should be able communicate with the Mod-80 computer through a PC at least. I will, however have to figure out how to get the Mod-80 TTY board to communicate at 300 baud instead of 110 baud.
Replaced all the 22 uF electrolytic capacitors on the boards with new ones. The new ones fit better and of course, the old ones could have been dried out by now.
Also removed all the components from the Mod 8-2 board and restored it to its original design condition.
Noticed that one if the transistors on the board seemed to have a melted lead.
Patched some trace cuts as well.
Received a call from Dave Kerr regarding the Mod 80. He says he has a few 1702 EPROMS and maybe a few odds and ends left, but not much else. Plan to meet him at HAMEX in Brampton on the 18th.
I finally figured out how to drive this teletype using an Arduino. Here is a short video showing it working.
Wrote letter to Dave Kerr (VE3FJK), the original owner of the Mod 80. Hopefully, he can answer a few questions I have.
Charles Baetsen holds a Bachelor and a Master's degree in Engineering Physics from McMaster University in Hamilton, Canada.