digital equipment corporation · maynard, massachusetts
My PDP-8/I at VCF East 4 (2007)

The retro computer hobbyist group MARCH hosted the Vintage Computer Festival East 2007 exhibit. I brought a PDP-8/I Computer with 8k core, along with AX08 laboratory peripheral, DF32 Fixed head disk drive, PC01 High speed paper tape reader/punch, ASR-33 Teletype, Tektronix 611 storage tube monitor, Calcomp 563 incremental plotter, and PT08 serial port for my exhibit. The PDP-8/I was the third model of PDP-8 computers. I also brought a DECmate III which was the last of the PDP-8 line of computers.

I was showing how the AX08 could capture a signal from a signal generator or a microphone, display it on the Tektronix monitor, and plot it on the plotter. I also had games people could play using the teletype. Using the PDP-8/I internal serial port and the PT08 I could also run multi user basic.

The machine hadn't had much run time since I restored it to operation. The machine was running for a couple hours while I worked on getting some demonstration software working when I heard a bang and started smelling that burnt smell indicate bad things have happened. I quickly powered the machine down then followed the smell and the sizzling sound to the 799 power supply that powered the peripherals in the rack. An AC capacitor on the ferroresonant transformer had failed. This was a few days before I was supposed to go to VCF with this machine. Luckly I had this supply also in my 8/E rack so I pulled the bad one out, clean up the leaked oil, and put the other one in. It seemed to be working ok with the other supply. After I got back I bought a new capacitor and fixed the original supply.

After I got to the show the AX08 display was distorted. I found a R107 inverter board was intermittent. Since I didn't bring any test equipment I had to track it down through the wiggle test (wiggle boards and see when symptom changes). Luckily I had a R107 in the board display which fixed the AX08 when I swapped it in. The board probably has a bad solder joint and didn't like the car ride.

The following picture links also have descriptions of what is shown in the pictures.

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DECmate III & VT52 ( 88K)
Plotter and Monitor ( 85K)
General Information ( 99K)
Tektronix 611 Storage Display Unit (104K)
PDP-8/I System ( 65K)
Car loaded rear (122K)  side (121K)
Failed Capacitor top (141K)  removed (120K)  good capacitor (114K)

This site also has some nice pictures of my exhibit along with the other exhibits.

Feel free to contact me, David Gesswein djg@pdp8online.com with any questions, comments on the web site, or if you have related equipment, documentation, software etc. you are willing to part with.  I am interested in anything PDP-8 related, computers, peripherals used with them, DEC or third party, or documentation. 

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