[SiriusHardware]

Well, let's think. Colin never mentioned the monitor doing this prior to the stripdown (he probably would have noticed it before then) so I think what we probably have here is a case of physical disturbance or change during the makeover rather than a new electronic fault.

I think something physical has changed - could be the position of a pot / preset, or the legs of a component 'connected' together by liquid which has not dried out, etc.

To begin with can you check that the thick rubberised cable leading from the tube cap to the top of the line output transformer is more or less as it was before, with the rubber cable kept well away from anything else on the way between the tube cap and the LOPT (Line OutPut Transformer).

Also try just reseating the display connectors at both ends of the cable which carries the video signals from the main board to the monitor. (Do that with the power off).

We'll need to find the right circuit for your particular monitor to see if there is a vertical hold or vertical position pot which may have just gone a bit noisy or had its value changed slightly.