PDP 8/L & 8/I G228 warning

David Gesswein djg at pdp8online.com
Fri Oct 16 13:37:35 CDT 2020

   Noticed in another thread an 8L is upcoming on the persons restoration
list. Making separate post so more visible. The G228's have a 20 uF 50V
electrolytic capacitor on them. I have had two short. When they short its
a race between the trace on the board burning up or the backplane 30 AWG
wirewrap wire burning up.  One was on an 8/I I was restoring where the
backplane wire providing the power burnt up at power on. Wasn't shorted
before power on. The other was I saw one G228 had a burnt track while I was
washing the cards in an 8/L. I had not applied power at that point so that
was old damage. Usage history is unknown.

As a minimum I would recommend applying current limited 30V to the capacitor
on each card out of the machine before initial power on. Low enough limit may
allow the capacitor to reform without shorting. The same part # capacitor is
still available for protective replacement. The capacitors don't read shorted
before power is applied. Unknown if they will short if the machine is powered
on periodically. 

I've head lots of reports of all the failures in 8/L's. I replaced the
one G228 and some bulbs but otherwise the machine was fine. It did need a lot
of cleaning and I did do my normal power supply reform and checkout.

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