> > Some of you may recall seeing me post about the VAXmate PSU failure. Thanks > to members of this list I found the failed part in the PSU and the PSU is > now working again. However, it looks like the PSU failed because of a > failure on the monitor board. There is a burning smell coming from it, > possibly the flyback transformer, but I am not 100% sure. I don't see > physical damage, but of course that doesn't mean there isn't a problem. When > I took the monitor board out again after this, I wasn't sure if the EHT lead > was making good contact with the CRT anode. The monitor board is described > in section 4.4 of this document: > http://bitsavers.org/pdf/dec/vaxmate/EK-PC500-TD_VAXmate_Technical_Descripti > on_1987.pdf >
Congratulations on getting your PSU failure sorted out. I suppose you realise this means there will be a line of people wanting you to look at our PSU problems the next time we meet up :-) > > I need some advice on diagnosing the problem, I have a few questions: > > 1. If the EHT lead was not properly connected to the CRT anode, could > that cause problems? > Possibly. I have VT220 terminal which was making a smell of ozone when it was running which I should have done something about but never got around to. This could have been due to corona discharge around the CRT anode connection or around the flyback transformer but I never found out. Eventually, it stopped working, drawing excess current from the 12V power supply. The flyback transformer appears to have been damaged. > > 2. Is there anything I can safely do with a bench power supply to > isolate the problem? > 3. Any other suggestions for diagnosing the problem? > One approach to testing flyback transformers seems to be to use a circuit that causes them to ring and observing whether the ringing is damped by shorted turns. I've never got around to trying this myself. > > 4. There is an outline spec of the flyback transformer in the section > 4.4.3.2 of the VAXmate technical description, what chance of finding a > "modern" replacement? > I wish you good luck with this. I never had any luck locating one for my VT220 :-( Regards, Peter Coghlan. > > I have posted about the PSU repair here: > > > > https://robs-old-computers.com/2020/04/18/vaxmate-h7270-psu-fixed-but-no-video/ > > > > Thanks > > > > Rob > >
