Set your multimeter to the DC voltage scale, range 60V.

Take the black lead and attach it to the case metalwork.

Take the red lead and do as follows: locate the two black electrolytic capacitors (they look like black tubes about a centimetre long with a lead coming out of each end) on the top rear of the display board. Touch (carefully) the capacitor lead nearest the inductor (the tiny black rubber tube sticking out of the board). Be careful NOT to short either probe against anything else - don't do this if you're pissed (or even just plain tiddly drunk)

You should read something like about 56V, max 63, min 46.

A little further explanation: the empeg has one main power supply on the motherboard. This produces a number of different voltages, 3.3V for the processor and RAM/FLASH, 5V for the peripheral devices (USB, Ethernet, IDE, Sound, etc), 10V (analogue, etc). However, it does not produce the high voltage needed for the display board.

The motherboard feeds three voltages (3.3, 5 and 12V) to the display board, with three in-line fuses. On the display board is a tiny switch mode DC-DC PSU that generates the required 60V HV for the tube (and therby conveniently localising it in the display board assembly for safety/isolation).

If this PSU goes a bit feak and weeble, then it looses the ability to drive the VFD properly and the tube starts to do weird stuff. Hence, yes, some tube faults are not necessarily a failed tube. However, if the tube looses vacuum, then it's knackered.

You need to measure the voltage first. I will post images after this post showing how to probe the display voltage.