When using beam finder, I can see a single vertical bar of 3cm height on the two thirds of the right hand side of the screen
The 7B50 does not have XY mode.
I tried to put the timebase into an input slot and I can also see horizontal bar when using beam finder
The 7B50 appears to work again when the plugin was cold. The beam then disappears on the 7B50 timebase after 15/20 seconds or so after the scope is switched-on