The interesting part is that as the trace sweeps, it is going backwards, or
from right to left. I verified this behavior by slowing down the sweep. The
dot indeed is going backwards.
Do you have another time base that tracks correctly, Left to Right? If not, it's possible that the wires to the horizontal deflection plate pins have been swapped. That would be an easy fix.
If you have other timebase plugins that sweep correctly, then you'll have to figure out where this 3B3 went wrong. I've got several 3B3s and the manuals, so I may be able to help if you get into this.
