On Fri, 19 Feb 2016 19:20:35 -0000 (UTC), Cursitor Doom
wrote:

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.

Well, at last there is a serious effort to actually record and report
real measurements. However, you may be misleading yourself.

Are you sure of the pin locations and their function on the
transformer? They will not likely correspond to the schematic
arrangement - which is arranged for functional clarity alone.

The transformer pin numbers are not identified on the schematic.

This is why it is much easier to make accurate winding voltage
measurements when the transformer is in-circuit, connecting to easily
identifiable schematic components and circuit nodes.

The voltages you report would be normal if the pin functions were as
listed below

13V.......60VAC
13V.......60VAC
3V........12V5
0V (gnd)
3V........12V5
1.8V......5V
1.8V......5V

The nonlinearity of the ratio is due to the increasing influence of
forward diode drop at lower voltage and the proportional loading
effects of differing currents on rectifiers, windings and output
filtering components.

Recheck pin function before jumping to conclusions.

RL