Whoa Partner !
What are you doing setting at 1500 Volts?
And 200 volts per horizontal division?
Drop it back to 15 volts.
And lower Volts per Division Horizontal.
If you have the switch turned to the diode?
There will be no steps for Diode.
Pins C and E only.
Raise voltage from zero and the line will turn upwards at the drop voltage.
The diode will turn on at .6 or .7 volts.
You need to reverse the diode in the holder you have voltage flowing wrong direction.
I got carried away with my first curve tracer also !!
But there is a complete Operation and Service manual available online.
Explains 1st time set-up.
Diode should look like..
Enjoy!
Also from the looks of the screen your unit CRT is fine.
I think I still have 6 curve tracers and none of them were free :-(