22 Feb
2012
22 Feb
'12
10:19 p.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org] On Behalf Of Tony Duell
Sent: 22 February 2012 20:55
To: cctalk at classiccmp.org
Subject: Re: Commodore 1581 repair conclusion
The very first 6800 I bought came with a failing carry between the two bytes
of the 16-bit registers. Very disconcerting as it was the first micro I had
ever made. However the supplier replaced it no questions asked...
Dave Wade G4UGM
Illegitimi Non Carborundum
I once had an 8088 that behaved very strangely,
it read the correct
opcodes from memory but executed something completely different
sometines. It turned out that the voltage between the +5V
pin and the 0V
pin was something like 4.65V. 0.1V too low a
voltage was
enough to make
it execute some code correctly and other code
completely
wrong. Since
then I always check the voltage at the
chip's pins if
strange things are
happening.
Very wise...
My PDP11/45 would run for about 30 minutes and then crash in
really odd
ways (odten asserting a bus grant for no good reason, things
like that).
I finally traced it to the fact that the +5V lien to the CPU
was sitting
at 4.3V. Sorting out (and adjusting) the appropriate 'brick'
in the PSU
fixed all the problems.
-tony