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Re: II+ beeps but then reacts very oddly
Linards Ticmanis wrote:
Hello Michael,
Michael J. Mahon wrote:
LS TTL is remarkably reliable and resistant to damage, which is why
it's always the *last* thing I consider as the source of a problem
(unless it's charred ;-).
Well, it was a 74S chip that was broken, not a 74LS. Are the S variants
less durable?
I have a lot less experience with them quantitatively, but I would
expect similar reliability. There are always a few "random failures".
;-)
And pulling chips wholesale and replacing them is the setup for a
mistake that will change a single-fault problem (easily localized)
to a multiple-fault problem that is very difficult to localize.
You'll have to admit though that the problem "absolutely no reaction at
power on" is not *that* easy to localize without a 'scope - or am I
mistaken in this?
True, a scope, or at least a logic probe, is almost a necessity.
For a "dead" Apple, I'd start by checking the supply voltages, then
the clock, then the reset to the 6502, etc., etc.
If the clock is present at the oscillator, but missing at the 6502,
then tracing techniques can find out where it vanishes, and that's
the culprit, and so on.
-michael
New, faster SUDOKU v2.0 solver for Apple II's!
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