Hi again,

I know I said I was going to mothball this scope for the time being, but
I keep thinking of new things to try and just can't leave the damn thing
alone. It struck me I ought to next check out the main transformer
because if that's toast, the whole psu might as well be binned. I think I
*may* be on to something.

Here's the circuit again:


https://www.flickr.com/photos/128859...in/dateposted-
public/

The transformer in question is T1801. I've pumped in a test signal into
its primary winding (2V p-p sine wave @20kHz Zs=600 ohms) and scoped all
15 remaining pins. Every single one of them is producing clean sine waves
at various amplitudes just as you would expect, except one, which is
giving a really thick, noisy trace. On the diagram, this is the 5th one
down on the right hand side (immediately below the 1kV out pin.) It's not
marked on this diagram, but is supposed to be 0V from another schematic I
have. Someone has replaced C1826 & C1827 at some time and the
replacements don't look good for more than 50V max to me, and that's not
enough since the pd across them will be much more (the parts list
specifies a 500V rating!) They're not showing short-circuit, so I'm
wondering if they've failed open maybe that could account for the
symptoms I've been getting: terrible noise in the primary circuit and the
rapid heating of R1814 (the 20 ohm power resistor intended to dissipate
the switching energy).
Any thoughts?