Upon the date 02:55 PM 4/25/00 -0700, Chuck McManis said something like:
The visual field guide lists it as ??? many other field
guides don't list
it at all. It was the answer to question I didn't know to ask. Its a
friggin' dummy load!
If you happen to come across a DEC "skunk box" also know as the BA213
chassis which was home to MicroVAX 3300 - 3900's and some DEC System
5500's, you'll notice it has two power supplies (one on the left and one on
the right). I was restoring a MicroVAX 3400 and thought it had a "bad"
power supply. As it turned out, without sufficient load these power supplys
will not "light up." So to fix that on the 3400 I plugged a Fujitsu SCSI
drive (known power hog :-) on to the disk connector and voila, the thing
So I've been looking at a couple of 3400's that were used as a cluster and
both of them had M9060 boards installed in the last slot. These boards
provide sufficent load on the supplies to get them to both turn on. _Very_
Moral of the story, if you think you have a "bad" BA213 chassis, try
loading up the power supply a bit, and if that works, find one of these
boards and plug it into the last slot!
Another of lifes little mysteries solved.
A rule of thumb I found back in the 80's (around the vintage of the BA213)
was to load a switcher with _at least_ 5% of its rated load current in
order for it to start and remain stable. Don't know about the -213 PSU but
5% is a starting point I would think. What are the values of the load
resistors on the M9060 and can you determine which supply lines they are
hung off? If the rated current for each PS line is known, one could cipher
the approximate load percentage the M9060 puts on the PSU.
Christian Fandt, Electronic/Electrical Historian
Jamestown, NY USA cfandt(a)netsync.net
Member of Antique Wireless Association