I had something similar with a VT220. I didn't get around to investigating it before the flyback transformer failed :-(
I can only suggest to run it for a short time with the cover off and the lights out while looking for any glows / discharges around the flyback transformer, the EHT cable, the EHT connector on the tube and the tube base connector. Regards, Peter Coghlan. Ps: Anyone got a flyback transformer for a VT220? > > i have a VT100 that is working fine (powers on, navigates setup, > saves/restores settings, etc) but has an unpleasant burning/ozone odor > coming from the rear of it. i suspect something is running hot but i am not > sure what, i do not currently have an IR camera in my hands- working on > that. the original power supply has failed and is currently in storage, so > the terminal is being powered by an ATX power supply and adapter board for > the time being. this eliminates the usual R27 as being the culprit. > > as best i can tell, the smell is strongest just above the power > distribution board, around the neck of the CRT. appreciate any suggestions > you might have!