I've just spent a couple of hours tracing out the power-supply
circuitry in this 'scope, particularly the HV supply driving many of
the CRT terminals.
Turns out the winding I thought was the HV winding, only shorted out,
is actually the CRT filament/heater winding. (I'm quite sure I've got
the CRT filament pins correct; they are the only two CRT pins that show
DC continuity.) I'm not sure whether it's a heater or filament;
there's a pin that could be the cathode (connected to one side of the
heater/filament, the most negative CRT pin found so far), but there is
an odd circuit which makes sense to me only as an attempt to compensate
for using one side of a filament as a cathode - there's a voltage
divider across one half of the 6.3V heater winding, with a HV cap
coupling it to the "cathode" side of the CRT filament/heater,
presumably to avoid the slight mains-frequency flicker that would
otherwise result.
The HV winding appears intact, and runs between one side of the B+
winding and the filament of one of the HV rectifiers;
===================
_oooo_oooo_oooo_oooo_
A B C D E
A-B-C is the centre-tapped B+ winding I found before. B is grounded
(the A and C points go to the plates of the B+ rectifier) and, based on
scaling up from the voltages I see, the A-B (and B-C) voltage is about
375VAC. D-E is the filament winding for one of the HV rectifiers. C-D
is a winding I was not previously aware existed; its design voltage is
about 500VAC (under the same assumptions about scaling).
The transformer's ground wire has DC connection to this winding, about
150 ohms to either D or E and something like twice that to C. Since
both this ground wire and B were grounded to the chassis when the
transformer was in-circuit, I conjecture that this is part of the
fault, and the ground wire is supposed to be isolated from all the
windings.
Interestingly, in view of the comments about how instead of a high
positive final anode voltage CRTs tend to run with a high negative
cathode voltage, it looks as though this does both: the final anode is
about as positive with respect to chassis ground as the filament is
negative.
I think I now understand all the power-transformer windings:
============================================================
_ooo_ooo_ooo_ooo_ _ooo_ _ooo_ _ooo_ _ooo_ooo_ _ooo_ _ooo_
A B C D E F G H J K L M N P Q R S T
A-B-C-D-E is as above. F-G, H-J, and K-L are the filament windings for
the B+ rectifier, the CRT, and the other HV rectifier. M-N-P is the
heater winding for most of the tubes. Q-R and S-T are the incoming
mains power windings (series for 230V, parallel for 115V). Add in the
chassis ground wire and this accounts for all the power transformer
wires.
I also suspect there is some effect operating to make my voltage
estimates come out high. The unregulated B+ supply (before the
resistor and 0B2) has a smoothing cap of 80uF 475V. This means the B+
winding, end-to-CT (A-B or C-B above) can't be higher than 335VAC,
probably less to allow some headroom, while my estimate put it at
nearly 400VAC, definitely high enough to overvoltage that cap.
Oh, and, yes, with the rectifier tubes pulled and the transformer out
of the circuit, I could feed it externally-provided power no problem.
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