Sick PDP-8/f: Need Diode Info!

From: Kevin McQuiggin <>
Date: Wed Nov 12 13:08:08 1997

Hi David:

> boards for decoupling capacitors, if their is one near each chip then that
> is what it is, any .01uf ceramic would replace it. It would be on the
> traces to the corner power and ground pins.

Well there ARE a bunch of them, they ARE near several ICs, and they are in
parallel with one side at ground. I think you're right.

I think I have found the major problem with my board:

The symptom I'm experiencing is that the DC OK H line, nominally 3.2V,
drops to 2.2V when the M8310 is inserted into the backplane, and then the
machine doesn't work anymore (not really, just can't RUN from the toggle
switches). This voltage stays constant at 3.2V either on an empty
backplane, or with all boards except the M8310 installed. Put the 8310 in
and the voltage drops to 2.2V.

I've traced this DC OK H pin to the input of a 7404 IC on the 8310 board.
With power off, the gate's input and output are seen to be at ground, i.e.
I think the gate is shorted. I wonder if you could look at your printset
and see where the DC OK H line actually goes and what happens after the
7404? I think this is a bad chip.

Thanks in advance,


> > If you need any more help email me >
> David Gesswein. >

Kevin McQuiggin VE7ZD
Received on Wed Nov 12 1997 - 13:08:08 GMT

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