M220B (PDP-8/I) schematics available

From: jpdavis <jpdavis_at_gorge.net>
Date: Mon Jul 14 00:33:01 2003

Robert Krten wrote:

> <snip>
>
>:-)
>
>In my case, the failure modes were as follows:
>
>2 chips failed with: grounding the PRESET line caused the Q
>to go high as expected, but when PRESET was left floating Q
>went low. [DEC leaves the PRESET and CLEAR lines floating on
>various modules, so I consider this a fair test].
>
>1 chip failed with insufficient +5 on the Q (or bar-Q, forget
>right at this instant) output. The measured output was something
>like 1.6V.
>
><snip>
>
>
That sounds like a design flaw. Even with TTL, unused inputs should be
tied to somthing.
What was the fanout for the Q /Q on the fried output?


Jim Davis.
Received on Mon Jul 14 2003 - 00:33:01 BST