[RogerEvans]

Have a look at the manual so that you can find your way around the scope safely. The standard procedure is first check all the low voltage power supplies for DC level and, if you can ripple, you could use the scope's vertical amplifier to check for ripple amplitude using AC coupling.

Is there a horizontal position control, and does that move the dot? Have you tried all the timebase ranges and also the variable control on the timebase. Is there a trigger light to show that the timebase is triggered and can you get line trigger to work?

This should begin to track the fault to the triggering, timebase generator or the X amplifier. It can be very useful to set the timebase to its slowest speed and then probe with the scope's vertical channel to see if there are any ramp voltages being generated by the timebase and where they disappear.

Roger