M220B (PDP-8/I) schematics available

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Thu Jul 10 14:42:00 2003

> > Is the 7474 a 'dog'? I've know a few TTL parts that were pretty bad,
> > mainly counters though. But a latch?
>
> This reminds me of a similar problem in the JC80 systems, where 74170
> chips would fail more often than anything else. I'd sure like to know what
> the cause of that was...

I can remember replacing many 7474s in the RK11-C when I was getting that
going. Oh, and a 7482 adder, which was impossible to find [1]...

More recently, I've had a lot of 74Hxxx parts (and yet more 7474s) fail in
HP98x0 calculators. I guess after 30 years I can't really moan...

[1] I do mean _iompossible_. I ended up using part of a 7483 that I stuck
to the flip-chip PCB dead-bug style and wired to the holes where the 7482
should have been. Runs fine...

-tony
Received on Thu Jul 10 2003 - 14:42:00 BST

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