M220B (PDP-8/I) schematics available

From: Ethan Dicks <erd_6502_at_yahoo.com>
Date: Tue Jul 8 10:03:00 2003

--- Jim Davis <jpdavis_at_gorge.net> wrote:
> Ethan Dicks wrote:
> >That's been my experience, too. I have replaced as many as 8 7474s
> >at a go to get an -8/L back on its feet. I don't recall replacing
> >any other chip, as a matter of fact.
> >
> >-ethan
> >
> 7474's Dead d flops? whats the story on that?
> Jim

Dunno. I can say categorically that they were failed chips. They
did not pass muster in a handheld TTL tester, and when replaced,
the PDP-8/L worked.

There was a mention on the list of a batch of 7440s that failed in
another M-series machine (might or might not have been an -8/L)
with the same date code.

Not sure why 7474s from the mid-to-late 1960s would be more fragile
than, say, 7400s. Perhaps the flipping and the flopping wears them
out faster than anding and oring? :-)

-ethan
Received on Tue Jul 08 2003 - 10:03:00 BST