This is a chronological log of the progress restoring
the University of Iowa's PDP-8 computer.
Entries are added at the end as work progresses. Click on any thumbnail
image to see full-sized image.
In preparation for the University of Iowa Tech Forum on June 6,
where artifacts from the Retrocomputer Lab will be on exhibit,
we put the cover on the Teletype for the first time since we
began work on it. Looks good!
We used an ohm meter to check all the diodes on the G107 sense-amplifier boards,
and found one of them that was bad, measuring as an open circuit in both
directions. The diode in question was D15 on the
in the Maintenance Manual.
DEC's part number for this diode is D668, and their
instructions in the Maintenance Manual (Table 10-1, page 10-5)
say to use two D-664 (1N3606) diodes in series.
|Bad diode replaced
As can be seen in the photo, showing the repaired board (bottom) and a board
with a good diode (top), the pair of diodes in series is a bit bulky. We
painted the transparent glass body of the diode with black paint because the
forward frop of this diode is used as a voltage regulator, and the forward
drop of glass-encased silicon diodes is notoriously light sensitive.