PDP 11 gear finally moved
ard at p850ug1.demon.co.uk
Sat Jul 18 14:31:11 CDT 2015
> Oh, sorry, didn't realize they used switchers for the PDP-11s.
There have been _many_ DEC PSU designed used for the PDP11. I think all of them used some
kind of switching regulator for the +5V line. A quick glance at the printsets will settle it..
> However I was talking with a friend of mine last night about my error,
> and he told me that the switching supplies for the PDP-11s were very
> unreliable back in the day. He often had to troubleshoot the machines
> back then. A common failure was caused by static electric shock to the
> machine would blow the supply. NO carpets allowed!!
That is (a) meaningless and (b) totally contrary to mine (and others) experiences.
It's meaningless because there are so many 'PDP11' power supplies. There are some which use
a mains transformer followed by step-down switching regulators. There are some which are more
conventional SMPSUs, rectifying the mains and chopping the 350V so produced. There are some which
are multiple versions of that in one box (and at least one of those has a switching supply running off the
350V DC rail which produces a single 36V output which is then regulated with more switching regulators).
I do not believe all those designs have the same failure modes, or responses to static damage.
However, I have worked on many PDP11s, with all sorts of PSUs. Now admittedly I am careful about
static, even working on bipolar circuitry. But not to the point of being silly about it. And I will state that I
have never damaged (or even caused to trip) a PDP11 PSU by a static zap to any of the output rails. And
if a static zap to the casing of the machine damages the supply I would want to check the mains earthing
(grounding) -- preferably before a fault causes somebody to get killed.
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