3 Mar
2006
3 Mar
'06
3:43 p.m.
I forgot to note, I replaced the H745 module with a known good one, it
didn't help.
-----Original Message-----
From: Julian Wolfe [mailto:fireflyst at earthlink.net]
Sent: Friday, March 03, 2006 5:40 PM
To: 'General Discussion: On-Topic and Off-Topic Posts'
Subject: 11/34a problems continue
Well, I've been messing with the 11/34 on and off now for a
few months as I feel like it.
The problem right now is that I have no light on the H745
power regulator. Both lights are on, on the two H7441s in
the other slots.
If I need to measure draw on the backplane to solve the
problem, where do I do it from? If on the power distribution
board or backplane, then at what points?
Secondly, do certain modules need to be installed to utilize
the H745's resources? (i.e. a device that uses -15vdc) or
should the light come on anyway from just being connected to
the power distribution board? I've tried with both those
modules in and removed from the system, and it didn't seem to
make a difference.
What do I need to do to diagnose this problem? It's really
driving me nuts.
Appreciating any help you can give,
Julian
8 Mar
8 Mar
2:23 p.m.
I just replaced that unit recently, so I really don't think it's at fault.
I suppose it could be.
-----Original Message-----
From: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org] On Behalf Of Tony Duell
Sent: Friday, March 03, 2006 6:44 PM
To: cctalk at classiccmp.org
Subject: Re: 11/34a problems continue
I forgot to note, I replaced the H745 module with a known
good one,
it didn't help.
I now suspect the +15V supply... It's produced by that PCB
under the mains transformer I think. I'll look in the prints.
-tony
4:28 p.m.
I just replaced that unit recently, so I really don't think it's at fault.
I suppose it could be.
Please stop guessing and start measuring!
In other words, stop swapping modules at least until you have some idea
as to where the fualt is. I've suggested the 15V supply is missing. I
might be right, I might be wrong. What I meant by that suggestion was
that if it was my machine, I would now stick a voltmeter on the 15V
supply to the backplane and see if it was correct or not. If it was, I'd
check it at the -15V brick too (been caught by bad connections too many
times!). If it was right there, I'd delve into the brick. If it was
missing at the backplane, I'd check back to the +15V regulator PCB, etc
You've swapped out a couple of parts so far I believe. Do you have any
reason to believe that the replacements are good? Only last week I had 3
disk drive spindle motors behave the same way (spin up, run for a few
seconds, then stop), and I thought the problem was in how I was driving
them. Not so, all 3 had much the same intenral fault!. These DEC power
bricks can suffer from dried-up capacitors, that could well be a problem
with your 'spare' unit too.
The first stages of tracing this fault properly need nothing more than a
multimeter. And I can't understand how anyone can hope to maintain a
minicomputer without that instrument.
-tony
4:40 p.m.
Well, actually the reason I replaced that particular module is because the
board blew. I got a used replacement from the DEC salvage guy I usually
deal with and it came back to life - sans the H745 coming up.
-----Original Message-----
From: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org] On Behalf Of Tony Duell
Sent: Wednesday, March 08, 2006 6:29 PM
To: cctalk at classiccmp.org
Subject: Re: 11/34a problems continue
I just replaced that unit recently, so I really don't think
it's at
fault.
I suppose it could be.
Please stop guessing and start measuring!
In other words, stop swapping modules at least until you have
some idea as to where the fualt is. I've suggested the 15V
supply is missing. I might be right, I might be wrong. What I
meant by that suggestion was that if it was my machine, I
would now stick a voltmeter on the 15V supply to the
backplane and see if it was correct or not. If it was, I'd
check it at the -15V brick too (been caught by bad
connections too many times!). If it was right there, I'd
delve into the brick. If it was missing at the backplane, I'd
check back to the +15V regulator PCB, etc
You've swapped out a couple of parts so far I believe. Do you
have any reason to believe that the replacements are good?
Only last week I had 3 disk drive spindle motors behave the
same way (spin up, run for a few seconds, then stop), and I
thought the problem was in how I was driving them. Not so,
all 3 had much the same intenral fault!. These DEC power
bricks can suffer from dried-up capacitors, that could well
be a problem with your 'spare' unit too.
The first stages of tracing this fault properly need nothing
more than a multimeter. And I can't understand how anyone can
hope to maintain a minicomputer without that instrument.
-tony
4:56 p.m.
Well, actually the reason I replaced that particular module is because the
board blew. I got a used replacement from the DEC salvage guy I usually
What do you mean 'the board blew'? Did the magic smoke come out (if so,
out of what?). Was there a hole burnt through the board, melted traces?
FWIW, unless the board was actually burnt, I think it would be
repairable. I once did something very silly to a H754 brick with the
result that 4 transsitors blew apart, one ressitor totally burnt up, etc.
And that brick is working again now.
And the +15V board is actually very simple. It's a linear regulator...
deal with and it came back to life - sans the H745
coming up.
I will ask you once more. Have you done any actual electrical tests on
this PSU?
-tony
6864
days inactive
6870
days old
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