29 Aug
2014
29 Aug
'14
12:44 p.m.
I have two failed VT100 (H7831) supplies in front of me. I gave up
trying to fix them because I think they're some kind of unholy circle
jerk-- where you can't have +12 unless you have +5 and you can't have +5
unless you have +12. I decided I will design a new replacement before
I spend any more time trying to fix these.
Are we talking abotu the same supply -- the SMPSU from a VT100 (and not
the VT101 supply which is very different)?
I find the VT100 PSU to be quite pleasnat to work on. In common with many
other DEC supplies of that period, the chopper cotnrol circuitry
(oscillaotr, etc) is on the output side of the isolation barrier and runs
off its own little linear PSU. So yo can remove the chopper transistor,
power up, and clip the 'scope wherever you like around the chopper
control IC.
-tony