LF: Microvax 3100 power supply technical information.

Dave Dunfield dave06a at dunfield.com
Sun Oct 21 17:07:56 CDT 2007

Hi Guys,

I have a "VAXserver 3100" which afaik is the same hardware
as a Microvax 3100. This unit has a bad power supply.

The power supply is labled: MODEL H7822-00

Anyone have schematics or other technical information?

In case anyone has run into this before - the symptoms:

This supply appears to be two "mostly separate" supplies
in one box. Both boards have connection to AC power.

One board generates +5, -5, +12 and -12v, which is the
sent via jumper wires to the second board - There it
appears to be monitored by a "power good" circuit, and
passes directly to the connector for the VAX mainboard,
and one of the two disk drive power connectors. All of
these rails look good.

The second supply generates +5 and +12v which is applied
only to the second disk drive power connector. This supply
constantly starts and stops - with or without a load. I
can see the output voltages coming on, then going off
over and over.

Since this supply drives only the second disk drive
power connector, the system shoud come up, however it
does not - I believe the reason for this is that the
power monitor is either holding the system in reset,
or providing a "bad power" indication which otherwise
halts the system because the second drive supply
voltages are not stable.

The connector to the VAX mainboard looks like this
(viewing end of power supply cable)

 -12 +5
 Gnd +12
 Gnd +5   [Key ]
 Gnd Gnd  [Tab ]
  +5 Gnd  [Here]
  +5 -5
  ?1 ?2

The ?1 and ?2 signals appeare to be control signals.
All power rails look good. With a supply borrowed
from a Vaxstation 3100 (smaller supply without the
extra drive connector/supply, but same main pinout),
I see 4+ volts on ?2 and some low but non-zero voltage
on ?1 - with the bad supply, both ?1 and ?2 are at

Can anyone tell me the names and description of
function for the ?1 and ?2 signals - I'd like to
know exactly what these are supposed to do as the
supply comes up.

Any other technical information and/or ideas would be
very much appreciated.


dave06a (at)    Dave Dunfield
dunfield (dot)  Firmware development services & tools: www.dunfield.com
com             Collector of vintage computing equipment:

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