VAX 4000-500 PSU Overload?
jnc at mercury.lcs.mit.edu
Fri Dec 11 07:46:50 CST 2015
> From: Jon Elson
> You should be able to safely power the machine with only a couple
> boards at a time to find which one is bad.
For debugging power supplies, a 'load module' (a card with only a bunch of
resistors on it) is invaluable. No trying to figure out where/how to connect
a large load resistor - just plug the board in.
DEC made several:
M7556 dual - +5V 1A -15V 375mA
M9060-YA quad - +5V 5A
M9713-AA dual - +5V 2.75A -15V .75A
The M7556 (at least) can be used on both QBUS and UNIBUS backplanes (since
they share the same pins for +5 and -12V (QBUS) and -15V (UNIBUS). Probably
all the others can be used on both buses, too, but check the pins they draw
The M7556 can be easily modified (with a few etch cuts) into a +5/+12V load
module, but the resultant board can _only_be used in a QBUS.
If you can't find any of these (there are none left on eBay, but other
suppliers still seem to have them), another alternative is to get a blank
prototyping board from Douglas Electronics (http://www.douglas.com/),
and add your own resistors.
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