remote adjustment boards for that are typically stable. clearly vertical deflection issues but why? could be a corrupt tda1771 or related components. caps, low b+ power to it, something else.
if you want it repaired reconditioned analyzed and taken care of / done feel free to use my services.
I think I have a U5000 like this. I would guess it's probably a resistor out of spec in the 600 section. I don't know if bad TDA1771 would look like this. I watching a zeno video, to test the vertical IC you just test the diode on the other side of the heatsink. if it's anything but junction drop or dead shorted (not your case) then the vertical IC is bad.
Going to remove the TDA1771 and replace with a known good one today. All resistors in 600 section test fine. This one is not pressing so it's going on to the back burner for now. I will test voltages on IC too when I get a chance.