Is the 74LS377 especially unreliable?

[ppppenguin]

[rant]
I've had the moody COW back on the bench. Again. I'm fed up with lugging all 30kg of it back and forth between the Broadcast Engineering Museum and home. It's almost impossible to work on in-situ, especially as we don't have the correct extender boards.

https://625.uk.com/tv_logos/bbc1_85.htm

Just about every fault has been a duff 74LS377. This is an 8 bit D register, a cousin of the commonplace 74LS374. The difference is that pin 1 is a clock enable on the '377 which allows you to do proper synchronous design. I've just changed 3 on a single board, making a total of 4 on that board alone. The rail voltage is about 4.9V and there's a slow start circuit on each board. All the logic runs from a chunky 60A switchmode PSU which is set to 5.2V to allow for the slow start circuit. The COW uses about 20A.

Fortunately we've been donated some 74LS377. Nowhere near enough to do a shotgun replacement, nor would I be willing to extract 100+ of them.
[/rant]

[Mike Watterson]

Maybe they have excessive current with a slow start PSU?

[ppppenguin]

It's not a very slow start, just preventing a high surge current and supposedly making things kinder when you put cards back into a powered system.

There are also LS374s on the board along with other LS TTL and loads more LS TTL on other boards. Everything else seems reliable, even the relatively small number of LS377s on other boards.

[Mike Watterson]

Maybe just "unlucky" or one batch of substandard. It's odd.

[ppppenguin]

Substandard batch seem the most obvious explanation. The other COW I've dealt with (at the Dulwich museum) hasn't had these problems. Though since all the COWs were probably made as part of one production run all the '377s might well be from the same batch.

[DrStrangelove]

What about the date code? That's generally an indication.