PSU for MicroVAX 3400 Not Faulty But Not Working - test-drb@ccmp.vtda.org

6 Jan 2011

...
  -----Original Message-----
 From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
 On Behalf Of Shoppa, Tim
 Sent: 06 January 2011 19:53
 To: cctalk at classiccmp.org
 Subject:

  A while back I mentioned that I have a MicroVAX
3400 with one of the
 H7868 PSUs not wanting to work (green light fails to come on). I have
 just tried the "faulty" PSU in a MicroVAX 3500 and it works just fine.
 I took a PSU from the 3500 and put it in the 3400 and it does not work
 in the 3400 either, only in the 3500. So clearly there is something
 else that is causing the problem and I am looking for suggestions,
 especially as the machine is in an awkward location and hard to
 dismantle speculatively. As a reminder this machine was working fine
 and I had not done anything at all to it prior to its failure, I had
 not moved it, changed any components or anything  
 Without sufficient DC load the H7868 will fail to start up.

 One supply goes to half the slots. There's a Q-bus card That is nothing but a
...
  bunch of power resistors for this situation, although
I Usually preferred to put in
...
  a KDA50 set 'cuz I had a bunch of those :-).

 Tim. 
(adding subject line back)

In this case I think the load should be there because it is the right hand
PSU that won't start, this powers the 6 slots on the right and these contain
the memory and CPU, so there should be enough load for the PSU to work.
There is indeed a resistor card in the leftmost slot, but the left hand PSU
lights up fine.

Regards

Rob