That's OK
if the flipchip sinmply brigns out each IC to different pins on
the connector (a lot of the simpler ones do),
A lot do. In my original post, I gave several examples for which this
A lto of the eariler/.simpler ones certainly do, so this is probably fine fo
the 8/I. A lot of later one, used in PDP11 devie cotnllers do not.
As with all debuging methods, you have to know the limtitations and only
use it where applicable.
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.
Yes. I don't happen to have one of those, nor have I noticed one for
sale. I already had the ZIF-socket PIC-processor-driven IC tester - I
They do turn up on E-bay from time to time. You want to get one with
plenty of the little boards with the 'good' ICs on them -- I think there
are jumper pins ot solder int to determine if a pin is an input or an
output too.
I think there's a bvoard with a socket on it, and switches in place of
the pins. A sort of 'universal' board. If you can get that one, it'd be
very handy.
FWIW, I don't have a logic comparator either. It's something I would buy
if it was cheap enoug has a curiousirt, but I doubt I'd use it for much
real troubleshooting. I've foudn that tracing signal;s with a 'scope or
LA is by fasr the quickest method.
Yes, there are failure modes for simple TTL gates that
won't be picked
up by a hand-held tester. In my experience, those are rare compared
to a chip with a blown input or output that just plain produces the
wrong output when the inputs are tickled. *That* will be found by the
tester and clip.
One that I kept on finding in the HP9800 machines was an IC (often a
74Hxx) where the upper transistor of the totem-pole hadfialed (or
somethign similar, thuse turning it into an open-collector gage. That's
eveil becuase an unonnected TTL input wil lfloat high, so thingd appear
to be working (and some lesser testers will pass the device), but of
coursew with no active pull-up on the line, the timing goes to h*ll.
Onvce I know what to look for it was OK, but the fist one took some finding.
-tony