digital equipment corporation · maynard, massachusetts
MARCH/RESISTORS Restoration (2014/2015)

This computer was donated to MARCH in 2008. See exhibit at VCF for the history of the computer. It was determined at the time that it should be restorable to operation though it would need significant work. The restoration was performed by David Gesswein (me) and Corey Cohen. This process was started at the end of 2014 as I completely disassembled the computer, cleaned it, removed existing paint and rust, and prepped it for painting. Corey Cohen did the finish textured painting. I then did the electrical restoration and some cosmetic restoration. The restoration was completed sufficiently to show the computer at VCF East 10 (2015).

The current status is the computer has one front panel bulb that needs to be replaced after the car ride and it needs further work so it will be reliable. It also has 14 cards from my spares or my machine. I ran out of time to troubleshoot the cards. Two of them have failures of delay lines that are no longer available so will require investigation on how to repair.

The computer had a Calcomp plotter interfaced to it. We have the plotter but not the interface. We need to decide on a suitable method for interfacing the plotter and restore the plotter. The plotter is a smaller version of my Calcomp 563 plotter. I created some slides on the restoration for a talk at the show.

The slides discuss what was last in the computer when used by the RESISTORS. The first 157 (octal) locations were overwritten due to deposit switch bounce on my computer. The octal dump is using od program where * indicates the memory contents for the missing address range are the same as the previous line. Binary memory contents, like the octal, have been converted to the lower 12 bits of 16-bit words for the convenience of more recent computers.

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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