Ian,
It is extremely hard to diagnose this, since you provided no details on exactly what or where your "screen" is.
OTOH, I would think this would be more of a coincidence. To me it looks like either an RF or a power supply
problem. It could be that whatever the "screen" is may be attached to the same power supply as the rig and/or
RRC and causing the problem when too much current is being drawn. I have actually seen that problem occur
quite a few times. If it is not the power supply and really not RF, then we would need to understand more about
your mysterious "screen".
73,
Mitch DJ0QN / K7DX