> -----Original Message----- > From: cctalk <[email protected]> On Behalf Of Rob Jarratt via > cctalk > Sent: 30 December 2019 18:13 > To: General Discussion: On-Topic and Off-Topic Posts > <[email protected]> > 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
