On Tue, 08 Mar 2016 12:35:07 -0500, JC wrote:

I have no idea what you now consider to be wrong with the PSU. Apart
from a resistor that in your opinion runs too hot even though its well
within its rating I seem to recall amidst your ramblings that the
voltage rails are correct?

Yes, they're fine. It's not *my* opinion that this is a poor design! I
posted the schematic to s.e.d and the designers there told me that. I've
said all along I know nothing about this type of PSU so I defer to those
better qualified. Having said that, the widespread evidence of charring
and soot residue that appear even worse in real life than in the photos
would seem to indicated that that is not a happy board. The rest of the
scope's boards are still pristine showing no sign of repairs at all.

It seems to me that the only fault was the diode which was pretty
obvious from the beginning. (Always check for previous repairs).

Nothing obvious about it! - apart from the rather poor replacement
technique. The problem with that replacement was very subtle inasmuch as
it wasn't recovering quickly enough at 20kHz. Nevertheless it was still
capable of functioning as a viable rectifier right up to 500kHz.

You persist in not using the correct manual, refuse to test it with an
appropriate load and won't put it in the scope to see if the scope
actually functions.

All the recent tests have been carried out using the actual scope itself
as a load - can't get any better than that. I won't put it in the scope
until that resistor is running cool. It's proximity to other temperature
sensitive components like diodes and its siting deep within the scope
uncooled lead me to believe that it is running far hotter than it should
be - and will be even worse in situ. That *might* just be a design flaw,
but I doubt it.