Don't know if it's similar to what you've
seen or not, but from my
experience testing M-series modules for the -8/L and -8/i, I've found
more dead 7474s and 7440s than any other type of chip.
When I was repairing m HP98x0 machines I noticed that 74Hxx parts were
significantly more likely to fail than plain 74xx parts. And I think the
74H40 and 74H74 were high up the list of those that had failed.
For my testing, I rigged up a 3M test clip
(
http://parts.digikey.com/1/parts/389650-16-pin-test-clip-3-row-space-923700…)
to a ribbon cable with two IDC headers crimped on one end about an
inch apart so that I could mount one IDC connector on each side of the
clip, then cobbled up an adapter for the other end of the cable from a
wire-wrap socket so that in the end, I had a cable that could clip
onto one IC and fit into the ZIF socket of a hand-held IC tester. I
would test my FLIP-CHIP modules out of the box, letting the tester
power all the ICs on the board but only fiddle the lines on the chip
under test.
That's OK if the flipchip sinmply brigns out each IC to different pins on
the connector (a lot of the simpler ones do), but surely on more complex
boards where the ICs are interconnected, you're going to have contentions
between the outputs of the IC tester andf the outputs of other ICs on the
board (which are being powered from the tester).
There is, of course, HP's logic comparator, which is a device that takes
a good IC of the type you are looking at, feeds it the same inputs and
the drive on the board you're tersting and compeaes the outputs of the
good IC and the one on the board. It then indicates which pins are different.
It's fie for simple gate ICs. It falls down on sequential devices unless
you can be sure they start off i nthe same state (suppose you use a
counter as a clock divider and don't bother to reset it to 0 on power-on.
The one in the tester may start off in a diifferent state, so that all
the outputs are differnet for evermore, even though the 2 counters are
workign perfectly). It also falls down if you have open-collector devices
wihci are wire-ANDed.
I am not sure eitehr the logic comparator or the IC tester will pick up
ICs that are 'going slow'. I've had S TTL fail in such a way that it
still perfoms the right function, but the propagation delay is much
longer than it should be. Trakcign that sort of fualt down is entertaining.
Personally,giiven all the restrictions, I am not sure either method is ant
faster than the old-fashuioned way of seeing what doesn't work and tracing
signals to find why it doesn';t work.
-tony