"Dave" wrote in message
news:Jwo0i.39373$KN6.7185@edtnps89...

When the scope is powered up, it has a white line which starts to cross
the screen from left to right. The line gets about halfway across, then
disappears and doesn't come back.

The centering is set to the left.

Set all knobs to mid position and try again. Set Sync to Auto.