AK6DN
Veteran Member
So, it finally happened on my PDP-8m. Insert key in the power switch, turn it to on, hear a funny mechanical noise, and the power key now turns freely to all positions (left/up/right) without any response from the system. Insert sad face here 
So I open up the box and find some plastic / nylon chunks laying in the chassis bottom near the power switch. Looking in with a flashlight and mirror I see the roundish oblong plastic / nylon piece on the rear of the power switch has disintegrated into pieces and fallen off the rear of the key shaft. More sad face
So time to disassemble the front panel and get to the key switch assembly. Not an easy task. The only thing worse in the PDP-8m is having to remove the power supply to work on it. But that is a whole other story with many sad faces. Had to do with repeatedly popping the AC breaker and ultimately finding the diode bridge on the transformer secondary had one diode shorted ...
I was able to collect all the pieces of the broken plastic (nylon?) switch part and superglue them all back together, put it on my high res flatbed scanner, and shoot an image (with a mm ruler for reference):
Then using a DXF drawing program, was able to fit a curve to the outline, and import the shape into Front Panel Designer, and get some copies made in aluminum (instead of plexiglass/nylon). Here is the result, compared to the original piece:
I had to manually drill and tap the hole for the setscrew (8-32x1/4) but that only took about 5 minutes or so per piece.
Here are the shots of the new piece assembled into a PDP-8m power switch assembly:
I bought a small lot of 5pcs of the part from Front Panel Express that were fabricated in 8mm thick aluminum (same thickness as the original DEC nylon part). They don't do full machining (mainly they do flat 2D front panels) so I drilled/tapped the 8-32 setscrew hole myself. Cost per part in very small quantity was about $16, goes down to $11 each in quantities of 20+.
But worth every cent to get the PDP-8m restored to fully operational condition.
And I suspect it is a matter of time before others suffer the same problem. The old nylon part I had in my system had become very brittle, and the stress due to the setscrew to secure it in place caused to crack and fail; mainly during my repeated on/off power cycling to isolate my power supply problem. My first attempts as using superglue for the repair were not successful.
Don
PS I do have a couple of spare parts I will let go for $20 each plus shipping. I will also provide the Front Panel Designer database to anyone that wants it if you want to source your own parts.
So I open up the box and find some plastic / nylon chunks laying in the chassis bottom near the power switch. Looking in with a flashlight and mirror I see the roundish oblong plastic / nylon piece on the rear of the power switch has disintegrated into pieces and fallen off the rear of the key shaft. More sad face
So time to disassemble the front panel and get to the key switch assembly. Not an easy task. The only thing worse in the PDP-8m is having to remove the power supply to work on it. But that is a whole other story with many sad faces. Had to do with repeatedly popping the AC breaker and ultimately finding the diode bridge on the transformer secondary had one diode shorted ...
I was able to collect all the pieces of the broken plastic (nylon?) switch part and superglue them all back together, put it on my high res flatbed scanner, and shoot an image (with a mm ruler for reference):
Then using a DXF drawing program, was able to fit a curve to the outline, and import the shape into Front Panel Designer, and get some copies made in aluminum (instead of plexiglass/nylon). Here is the result, compared to the original piece:
I had to manually drill and tap the hole for the setscrew (8-32x1/4) but that only took about 5 minutes or so per piece.
Here are the shots of the new piece assembled into a PDP-8m power switch assembly:
I bought a small lot of 5pcs of the part from Front Panel Express that were fabricated in 8mm thick aluminum (same thickness as the original DEC nylon part). They don't do full machining (mainly they do flat 2D front panels) so I drilled/tapped the 8-32 setscrew hole myself. Cost per part in very small quantity was about $16, goes down to $11 each in quantities of 20+.
But worth every cent to get the PDP-8m restored to fully operational condition.
And I suspect it is a matter of time before others suffer the same problem. The old nylon part I had in my system had become very brittle, and the stress due to the setscrew to secure it in place caused to crack and fail; mainly during my repeated on/off power cycling to isolate my power supply problem. My first attempts as using superglue for the repair were not successful.
Don
PS I do have a couple of spare parts I will let go for $20 each plus shipping. I will also provide the Front Panel Designer database to anyone that wants it if you want to source your own parts.
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