The DEC M9060 board

From: Christian Fandt <>
Date: Sun Apr 30 12:33:51 2000

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_
>handy gizmos.
>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.

Regards, Chris
-- --
Christian Fandt, Electronic/Electrical Historian
Jamestown, NY USA
        Member of Antique Wireless Association
Received on Sun Apr 30 2000 - 12:33:51 BST

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