Older PDP-8 repair (was Re: new here)

On Tue, Apr 26, 2011 at 7:34 PM, Michael Thompson <michael.99.thompson at gmail.com> wrote: Did you have to do any work on that -8/S? I have one that needs a lot of replacement bulbs and some sleuthing in the "lock" circuit (the switch is fine, but the machine behaves as if it's always in "lock" mode). I've done lots of work on M-series machines like the -8/L and -8/i (it's where I got my start with 12 bits), but virtually no debugging of the older logic. I built a simple M-series FLIP-CHIP tester with a DEC backplane socket and an 6821 PIA, but it was straightforward to abstract different arrangements of inputs and outputs for different modules. I haven't done the homework to see how many types of R/S-series modules are used in a Straight-8 or -8/S, so I'm not even sure how difficult it would be to make a comparable logic tester. I'd like to automate the testing to the point where I could at least plug in a suspect module and either flip some switches or type some commands to exercise the inputs and monitor the outputs - yes, one can debug pre-TTL machines with a lot of clip leads and an oscilloscope, but I'd like to abstract that one level to see what boards need detailed attention. Has anyone ever considered building an automated or semi-automated R/S-Series module tester? Did it get further than musings and drawings? -ethan