M9060 - test-drb@ccmp.vtda.org

22 Jun 2010

Rob Jarratt [robert.jarratt at ntlworld.com] wrote:
...
  I have a MicroVAX 3400. It uses quite a lot of power
compared
 to my other MicroVAXen (about 180-200W). It has an M9060 Load
 Module installed and I understand that this is needed to give
 the power supplies enough load to work correctly. However, if
 I have enough stuff already in the machine then it would seem
 that this module is just sucking up power needlessly. How
 much stuff do you need in the machine to make the M9060
 redundant? At the moment I have a KA640 CPU and a KA655 CPU,
 two 16MB memory boards a DESQA and the TK70 controller. I do
 not yet have any DSSI disks for it, nor do I have a KFQSA,
 but the KA640 has DSSI built in. 
Each of the two PSUs needs to be sufficiently loaded to work and if 
either is not happy the system shuts down. So if you arrange to have
enough load in slots 7-12 you can put the load board to one
side for now.

However, the CPU and memory need to be in the first few slots
(iirc) and I very much doubt that a DESQA and a TQK70 are
enough to keep a PSU happy. If you had a KDA50 in there
you'd be fine, I would guess.

...
  Incidentally, anyone know why this machine has two
PSUs if
 they are not (as I have read somewhere) redundant? 
I assume that there was not a single PSU around that could supply
all 12 slots. There are at least two BA200 series enclosures:
the 12 slot one you have and a smaller 6 slot one. I assume that
a single power brick is enough for the smaller enclosure and
that it was simpler to have two power bricks in the bigger
enclosure rather than go off and design a more powerful brick.

Remember that when these things were new 180W was chicken feed
compared to the more powerful machines of the day (like the
VAX 6000 series).

Antonio