Restoring Sony DXC-1820P cameras, suggestions

[platux]

Dear all,

I've been collecting professional video cameras from the 70s to 90s for quite some time now. I love their design, construction, build quality and the organic image look and quality they provide. You cannot believe how people born in the digital era I deal with like them, from all points of view, and ask those camera to me for video productions. Analog video reinassance at the corner? Hope so!
I like to restore all the equipment I have, aesthetically and functionally, but my experience with tube cameras and electronics in general is limited. I hope you guys who have a lot, from what I've read in the forum, can give me some advice.

So I have these two Sony DXC-1820P cameras (single 2/3" SMF Saticon tube, early 80's, ABO) coming from different sources, which exhibit the same issue:

After the camera is turned on and still "cold" everything is fine, the image is stable, but after 1 minute or so the image start to slightly shaking vertically AND flickering
If the camera is shut down and re-started the issue persist. it gets worse as the camera is left on. then if shut down and left off for some hours the issue disappears.

See the video output from the camera here (file can be downloaded at its full quality). notice the vertical and signal intensity jitter:

https://drive.google.com/file/d/1IP6-cUHt_Kuis4S1JLV9w96Hi6EIG18j/view?usp=drive_link


So I´ve spent quite some nights investigating and probing, I have the schematics (here), and checked the following:

- signal coming out from the saticon tube: it already jitters in intensity and time as the image, so I discarded issues in the processing board. must be something in earlier stages

- camera power is stable, tried with different power supplies, and also added a low pass filter to the power input
- vertical and horizontal deflection signals: OK
- vertical and horizontal deflection sawtooths: OK, perfectly synched with HD and VD signals, no jitter etc.
- beam focus circuit: seems OK, stable voltage at the coil entrance, also substituted the high-power transistors who drive coil current, issue persist.
- 5V and -5V for the focus coil seem stable (pending substituting last high power transistor)

so my suspects start to focus on the high-voltage circuits for the tube that drive the various grids:
- K discharge circuit (although its input signal is stable)
- G1, G2 voltage etc.
but I did not check all of that yet, as I'm quite hesitant
Also I'm not imaging an unstable voltage in the grids might cause a vertical jittering (?)

In your opinion and experience, any clue on which area the issue might be in? is this a common type of fault?

Any suggestion appreciated, thanks in advance