pdp8/L restoration time, part 1: switches

Chris Zach cz at alembic.crystel.com
Sat Dec 4 15:46:01 CST 2021

I've decided it's time to fix my second pdp8/L. First one is missing (I 
think it's at the bottom of the closet) so I'll work on this one for awhile.

First problem: Testing the lamps and switches. If the switches don't 
work or the lamps are out it's not going to be easy to troubleshoot. 
Currently I'm missing 5 of the plastic switches, and I have 2-3 switches 
with a broken pivot.

Since I was going to need new plastic switch covers I fired up the 3d 
printer, downloaded the STL file for making them (thank you for putting 
that up!) and ran off a few for testing. It helps a lot to set the 
bridge angle value to 60% or so, that allows a nice solid bridge for the 
two "teeth" that engage the rocker switch. Also don't bother with PLA: 
The plastic pivots are too weak and break pretty quickly. Use PETG, 
which requires higher heat (240 instead of 200 at the head and 70 
instead of 60 at the base) but it is more than strong enough for the 
pivots to go in without issues.

Testing the switches I found that one of the data/address switches was 
reading high ohmage (20) when closed in the down direction and two of 
the data entry (spring loaded) switches were intermittent. Sprayed in a 
bit of Deoxit, and they now switch cleanly and without bounce. That 
would probably have driven me crazy if I tried to test with that.

Next step: Check out the power supply.....


More information about the cctalk mailing list