[CCTECH]74123 woes

From: John Honniball <coredump_at_gifford.co.uk>
Date: Mon Jul 15 14:00:00 2002

Jim Battle wrote:
> Anyway, I found and fixed the first problem: one of the satellite circuit
> boards on the persci had a tantalum cap that had a dead short, taking out
> the whole +24V power supply...

Yes, that's a typical failure mode for tantalums!

> Secondly, I haven't done board-level design in more than 10 years, but from
> what I recall, 99 times out of 100 when I thought I had tracked down a bug
> to a back chip, it was something else (then again, that was during design,
> not just working on ostensibly correctly designed boards).

Until recently, I'd have blamed something other than a 74 logic chip
just going bad. However, I've seen a few chips do just that in RL01
disk drives, which must be about the same age as your chips (late

So, I'd say it's possible that the 74123 has just ceased to function
"all by itself". Due to age, that is, not due to external factors.
In the end though, it's up to you to decide whether you suspect chip
failure enough to warrant replacing it (with all the associated taking
apart, soldering and putting together again).

John Honniball
cctech mailing list
Received on Mon Jul 15 2002 - 14:00:00 BST

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