Hi all,

I've completed my tests of the main transformer and am now 99% certain
that it is the cause of all the problems I've been experiencing with this
old analogue scope. It's clear there's something very wrong with the
large, multi-tapped output winding. Here's the schematic again:

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

I removed ALL connections from the transformer. ALL the other output
windings are giving exactly the outputs I would expect from a given
input; it's just the long winding on the lower right hand side that's
giving nonsense outputs. As you can see, the centre tap is grounded and
there are 3 tapping points either side of it. When injected with a 20kHz
sine wave of 50V p-p to the primary winding, the peak-to-peak outputs
from the problem secondary at each tap are as follows (from top to bottom)

13V
13V
3V
0V (gnd)
3V
1.8V
1.8V

I would have expected these voltages to be symmetrical either side of the
0V centre tap, but as you can see, this isn't the case at all. I can only
conclude from this, to use a technical term, that this tranny is ****ed.
If there's something obvious I've overlooked (which I doubt) please feel
free to point it out. Otherwise I'll be opening it up to perform an
autopsy over the weekend.
Thanks again to everyone who tried to help.