Usually the power supply isnt regulating & triggering HV shut down ( HVSD )
Could also be over current in HV such as a bad FBT.
To diagnose safely you need a variac & AC amp meter.
1) unplug the degausser.
2) hook meter in series with AC line.
3) plug in to variac set at apx 90 V
4) turn on but DONT let the meter go above 1 amp.
If it draws over an amp its 95% HV.
If it stays on its 95% power supply.
Sometime a set wont start at 90 V. turn up a little at a time till it starts.
73 Zeno
LFOD !