PDP-12 Restoration at the RICM

Michael Thompson michael.99.thompson at gmail.com
Sun Jun 14 08:53:59 CDT 2015

Dave Tumey sent us a new rubber hammer for the Teletype. This is the part
that pushes the print drum against the ribbon and paper to print. These are
newly molded parts that have not been available for decades. Works very

The ripple on the power supplies is still going lower as we put more run
time on the system. The power supplies are now within spec.

Warren wrote a better memory checkerboard program that shows the bits that
were being picked up or dropped in the MQ register. We tried adjusting the
STROBE FIELD 0 delay about +/- 100nS, but there was no setting that
resulted in completely working memory. Changing the delay did change the
location and number of bits that were picked up or dropped. Since the
failing addresses were all above 1000 we tried replacing the G221 modules
in slots C07 and C08. There was no change. We suspect that we have a
problem in the inhibit circuits.

Warren made an Arduino based programmable baud rate generator that works
for both serial ports. After some debugging, it works nicely.

The donor dropped off the work table that goes in front of the PDP-12. We
need to loosen the rusted feet so it will fit under the front panel.

Michael Thompson

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