11/34a problems continue

[Julian Wolfe]

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
>