Curiosity about power supplies (BA11)

Tim Shoppa tshoppa at wmata.com
Mon Mar 27 12:17:40 CST 2006


Julian asked:

> Okay, so I was thinking, would it be possible to replace the
regulators and
> whatnot in a BA11 with several standard PC power supplies?  Obviously
there
> would be adjustments that need to be made, but considering the DEC
units are
> now 20+ years old and the out-of-service modules may have dried up
caps,
> would this not be a possible option?

"BA11" covers a lot of chassis/backplane combinations, both Q-bus and
Unibus and not really any bus. I suspect you're talking about the 10.5"
high Unibus box. Dried up caps in the modules are far from a fundamental
difficulty. Compare that with re-doing the power bussing on the
backplanes
and replacing a couple of caps seems downright easy :-).

Not all the backplane signals are drop-in compatible with PC-clone power
supplies, but when third-party manufacturers used PC-clone power
supplies
for Q-bus chassis the extra signals were easily generated with a little
board.

On the Unibus, you probably need at least a token 15V supply and maybe
one that can give substantial currents (depending on what boards you've
got.) Some of those will run off +12V just fine, but others won't

Look at Strobe Data's Unibus backplane for an example of one way to
approach the problem: http://www.strobedata.com/home/ubus.pdf

One warning: few "350W" PC clone power supplies are actually capable of
pumping out half that much power. There are good PC-clone supplies but
at
that price point the "industrial" switchers are not too far off in price
(and are
far more flexible in terms of configuration.)

Tim.



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