Tektronix 466 storage scope lost horizontal
I recently bought this Tektronix 466, and after only a few minutes of using it I suddenly lost the horizontal but still get some signs of life when moving Xpos and a vertical line when a signal is applied. But other than that it’s just a dot(I have been careful to keep intensely at its lowest and spend the minimum time with the dot in one position to avoid burning a hole)
I immediately checked the voltage rails, and since then I've been checking capacitors and probing transistors, mainly around the sweep generator and reset circuits. I can see some activity from the sweep generator, but I haven't been able to work out where the fault is.
This is my first time attempting to repair a solid-state oscilloscope (I've previously worked on several valve/tube-based scopes), so I'm finding this one quite a bit more difficult to troubleshoot. I'm starting to run out of ideas and would really appreciate any advice on where I should be looking next.
I've attached a video showing the scope in use.
If anyone has experience with the 466, or can suggest some specific tests or points I should check, I'd be very grateful