> All this lab testing was done after all the options
> at the customer's place were exhausted, and that included rack grounds, n=
ew
> cabling, new distribution amp, new monitor on rack, new player vcr, his
> electrical supply grounding, eliminating all other equipment which may ha=
ve
> caused the problem.

We had an international telex exchange that served the whole of NZ as
its international gateway. As I recall there were two redundant system
with a pair of redundant PDP11/34 computers in each. There was a cross
over switch in the middle that could flip memories and maybe
peripherals between the two halves. Like an A/B switch on steroids.
(Been a few years - maybe just 2 computers). Anon ... The exchange
developed a crash-and-reset fault that happened up to days and as
little as 5 minutes after a restart. The half of the system on live
load crashed and transferred control to the standby while it rebooted.
We tried everything and then some. Swapped in spares, swapped system
parts and compared symptoms. There was another telex exchange in
Christchurch (about 1000 miles away) and we ended up freighting
processor units between exchanges.

After many months the fault was isolated to a bus cable connecting the
two halves via the A/B switch. No apparent fault, visual inspection OK
and DC tested OK. How and why it caused the crashes unknown.   Many
months to find. " when things decide to be perverse, they want to stay
that way." :-)


 Russell
--=20
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