PDP-12 Restoration at the RICM

Michael Thompson michael.99.thompson at gmail.com
Sat Jun 20 19:38:31 CDT 2015

The LINK indicator light on the front panel of the PDP-12 failed two weeks
ago. The indicator light bulb failed, briefly shorted, and destroyed the
transistor that turns the indicator on. An new transistor and bulb, and all
is well.

We have been chasing a transient problem in the PDP-12 core memory for a
few weeks. We checked the timing last week, and it was OK. This time we
checked the core voltage and it was a little low. We increased the core
memory power supply voltage until the checkerboard starting working without
errors. Next time we will explore the high and low limits of the core
voltage to find a reasonable center voltage for both core stacks.

The next step is to run all of the processor diagnostics and make sure that
everything is works. If the diags run OK, it is time to fix the TU56 tape
drive and see if the drive and controller work.

We visited the RCS/RI crew today to look at their LINC-8 and both PDP-12s.
Both PDP-12s are earlier than ours. One has floating-point and an RK05. The
other has a really interesting RAM buffered AD converter.

Michael Thompson

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