15 Jun
2003
15 Jun
'03
7:55 a.m.
Really? I have an H740 power supply sitting inside the
chassis of a
PDP-11/05 that wants to argue with you. As it is, half the +5V regulator
has been removed, and is going to have to be replaced. It's not going to
cost that much, but still, I fie you to call that a "replica". The
I see no problem in rebuilding a PSU, but I'd want to keep to the
original design if at all possible...
important part isn't "Oooh! Shiny old
collectible!", it's "watch me make
the binkenlights do foo after I toggle this program in on the front
panel." There's a PDP-11/45 that my friend and mentor essentially rebuilt.
New power supply, grafted-on LTC, etc. Yeah, you can argue that replacing
a power subsystem is somehow devaluing the system in some way. The system
Yes, actually I would claim that. The PSU _is_ part of the computer.
will be worthless, though, if you use a period power
supply. When linear
Why? My 11/45 (early version ,too) is still running on the original PSUs. All
I've had to do is rebuild one -15V brick...
supplies fail, they can do interesting things , like
toast your logic.
FWIW the 11/45 PSUs (and AFAIK all PDP11 PSUs) have switch-mode
regulators, at least for the +5 and -15V lines. YEs, they can fail, and
yes, in theory they can put overvoltage onto the logic, but DEC put
crowbars everywhere.
I've had mainns-side SMPSUs fail too, and put nasty HV spikes on
the output (an open-circuit or high ESR output capacitor will do that!),
and I've had regulation circuits fail in modern SMPSUs...
Perhaps it's just me, but I've had a lot more problems with relatively
modern 'commodity' PSUs that with the units in 1970s minicomputers. And
at least the latter come with printsets so I have a hope of fixing them.
What is the point of having a pristine, unmolested
logic board of
burnt-out chips? A different friend of mine recently acquired a PDP-10
That's why you alwys check PSUs on dummy load after installing the
machine or workign on the PSU. And why you check the crowbar (NOT by
triggering it! -- with a dummy load, put a lamp in series with the SCR
anode and then twaek up the PSU output to ensure it will trip -- assuming
the PSU can be turned up that high). In fact I'd probably replace the
crowbar components with new, tested, parts in any really rare machine.
-tony