13 Dec
2015
13 Dec
'15
3:21 a.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Maciej W.
Rozycki
Sent: 11 December 2015 01:48
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: VAX 4000-500 PSU Overload?
No leaking ChemiCon SXF-series capacitors inside? They seem to suffer
from some kind of design or manufacturing defect and consequently the
electrolyte gets through the seal eventually even in parts never used. A
number of DEC PSUs have these capacitors, including the H7874 PSU which
BA430/BA440 VAX 4000 cabinets use.
Just opened it up and there are indeed leaking caps, the brown ones. There
is also a strange deposit on a couple of screws (picture here:
http://1drv.ms/1micVN7), but the screws are nowhere near the leaking
capacitors. Any thoughts on that?
<SNIP>
Unfortunately replacing the parts is not easy as
heatsinks block access
to the
soldering pads and you need to desolder main
rectifiers first to gain
access.
You need to clean any electrolyte spills too as they
will cause corrosion
and
shorts.
Yes, I have had one of these PSUs apart before and know how horrible it is
to get at these parts. I will however go ahead and replace these caps.
I observed similar symptoms with the failed PSU as you do: it started up
briefly, enough for diagnostic output to start coming from the system
through the console port, and then within a couple of seconds the PSU shut
down.
I don't have an easy way to apply test loads to all the outputs at the same
time. Is it possible to remove the final output boards for each "half" of
the output and test one at a time without causing the PSU to shut down?
Thanks
Rob