PDP-12 Restoration at the RICM

Michael Thompson michael.99.thompson at gmail.com
Mon Aug 10 19:41:12 CDT 2015

We found a shorted diode in one of the rectifiers in the +/-42VDC supply in
the VR14 that was causing the main fuse to blow. The donor of the PDP-12
gave us a spare so that was an easy fix.

We reinstalled the VR14 in the PDP-12 and ran the display diags. The VR14
display actually works!

We found a open trimpot for the gain on the vertical flip-chip. We swapped
the horizontal and vertical flip-chips, adjusted the gain trimpot, removed
the flip-chip, and added a fixed resistor with the same value for now. The
display when running the diags looks very nice and crisp.

We booted LAP6-DIAL and could display a listing of the files on the tape on
the VR14 monitor. After about 20 minutes of running nicely, the TC12 went
back into the mode where it could not find blocks. Oh well, more debugging
to do.

Michael Thompson

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