Rob Jarratt robert.jarratt at
Sat Mar 28 12:21:23 CDT 2020

I have posted here a couple of times because I have a failed VAXmate PSU. I
have just posted a little bit more information here:
270-psu-failure/ with some scope traces and a greatly improved schematic.
Although the schematic is likely to have errors still. Unfortunately, a
stray scope probe ground lead blew the fuse so now I have to wait for a new
fuse to arrive before I can continue work.


I would really like to know if all the spiking I am seeing is to be
expected, and any suggestions why it appears to be detecting an overcurrent?
There do not appear to be any shorts on the secondary side, but that could
be wrong of course. I don't know if a genuine short anywhere would cause it
to trip the SCR quite so quickly (within 20ms of the switching transistor
starting to switch).


Any thoughts gratefully received.





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