A little progress on my side.
I started testing the voltages, while still powering it from 12 V from my bench power supply.
Normal current consumption is about 500 mA.
As I'm powering it from 12 V DC, I currently neglected the 230 V power supply, which is Assembly I in the unit.
Funny thing: While the scope was powered on, something clicked inside and the current jumped to 1.1 A.
At the same time, the green power indicator (battery operation) on the front panel switched off because of the current limit of the PSU. (That's normal behaviour in order to indicate low battery.)
Not sure what that was. Didn't occur again during the test.
Also, the whining noise of the transverter came up now and then.
Now for the voltage:
Currently it seems the transverter is not working. All its voltages are far below spec and the calibration signal (20 mVpp square wave) is missing.
My measurements: (measured // expected)
A 4.2 V // 12 V
B -3.2 V // -10 V
C 28 V // 85 V
D -134 V // -350 V
E -164 V // -450 V
F 0.2 V // 20 V
E-F -170 V // -470 V
I-H 0.0 V // 6.3 V (I suppose that's the heater voltage for the tube)
G -9.9 V / -10.0 V (the only one present)
K-L 0 // 20 mV square wave
I suppose the transverter assembly is the one to start with.
As for the two capacitors on top of the transverter unit:
The larger Tesla unit is an electrolytic cap with 100 uF and I think it's C210.
This one measures okay.
The other one is a 10 nF, and it should be C202m related to the screen lighting circuit.
This one appears to be open. Will have to desolder that one to be sure.
Edit:
While reading the troubleshooting section in the service manual, I suspect that the electrolytic caps in the transverter section are gone, plus some of the rectifier diodes.
So I'm going to have to remove that section and start swapping components...