repairing early HP calcs
ard at p850ug1.demon.co.uk
Mon Dec 19 18:15:58 CST 2005
> I think for example in the TRS 80 /I a 7400 with a defective unused
> gate was used because it was cheaper than a working 7400.
I don't recall that, and I've worked on most TRS-80s, and read the
schematics. Of course there are unused gates that could be defecive.
I remember a UK company called Bi-Pak. They bought up defective ICs,
tested them , and sold them. They did sell things like TTL quad-gate
packages with only 3 good gates. Problem was, as we all found, those 3
gates quickly failed in use.
 The tester was built from telephone relays and selectors. It ran at
about 1Hz. Plenty of chips passed that test and failed at more reasonable
speeds.... Don't ask how I found that out.
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