CRT oscilloscope issue

[frankX0]

I have a Leader LBO-310A oscilloscope which was working fine until recently.
It now produces "extra" lines which go from the actual beam position on the screen to a point in the middle of the CRT. Both X- and Y-channels work properly,
The photos show the scope in XY-mode, where I can freely move the position of the actual measurement, but with the addition of the extra lines.
I have the service manual with the schematics, which does not look over complicated. But I also cannot deduct which part is causing this failure.
Help is appreciated!

[David Hess]

That looks a lot like ripple on the supply voltages because the aluminum electrolytic capacitors have worn out.

[bob91343]

Bad CRT maybe.

[frankX0]

I would not call this DC (see attachment). Nor would I call this ripple btw.
The 47uF/315V elco's are gone.
Thanks for pointing me in the right direction!