PDP 8/L & 8/I G228 warning

Jay Jaeger cube1 at charter.net
Fri Oct 16 14:57:12 CDT 2020

On 10/16/2020 1:37 PM, David Gesswein via cctalk wrote:
>    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.

Thanks for that warning - my 8/L and likely the PDP-12 as well
appreciate it.  ;)

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