-----Original Message-----
 From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Rob Jarratt via
 cctalk
 Sent: 30 December 2019 18:13
 To: General Discussion: On-Topic and Off-Topic Posts
 <cctalk at classiccmp.org>
 Subject: Replacing Electrolytic Capacitors on VAXmate Video Board
 I have my VAXmate in pieces at the moment because the PSU has failed. I
 am still working on finding the fault there, although it seems to be the
 crowbar circuit that is shutting it down. To work out the problem I am 
going
  to buy a DSO (Rigol DS1054Z) as my regular scope is
analog and not much 
use
  in detecting one-off events. It is an odd fault
because there was a 
definite
  bad smell after the failure, but I can't find any
blown components. 
Whatever
  blew up has presumably taken something on the PSU
board with it, but I
 don't know what yet. The PSU shuts down even with none of the other
 VAXmate boards attached (and using a scratch HDD as a load).
 Anyway, while I have the machine open, I thought I would look at the video
 board capacitors too. Before the PSU failed, I noticed a bit of an 
occasional
  wobble in the screen image and a narrowing of the
image at the top of the
 screen. I have measured ESR on all the electrolytics. All the larger 
capacitors
  seem to have a low ESR compared to the table printed
on my ESR meter,
 some of the small ones (15uF/16V sort of size) have an ESR closer to the
 values printed on my ESR meter. I don't really want to replace everything 
if I
  don't have to, but equally I don't want any
kind of failure to ruin an
 irreplaceable component like the transformer. Should I just re-cap the 
lot, or
  just the physically smaller capacitors?
  
Does anyone have any thoughts on this? I am not sure how extensively to
replace the electrolytics.
Thanks
Rob