Peter, thank you for the reply! i had to wait a bit for it to get dark enough, but i just checked and i could not see any visible arcing inside the chassis when the terminal is powered on. there is a slight buzzing noise coming from the problem area but i suspect that is normal. i did notice something new and potentially enlightening though, this time when i turned the terminal on i could see several lines stretching diagonally across the screen that were not there before. i also checked the transformer(?) above the power distribution board while the unit was powered on, it does not seem to be overheating. On Tue, Dec 20, 2022 at 1:09 PM Peter Coghlan via cctalk < cctalk(a)classiccmp.org&gt; wrote:

I'm not familiar with the VT100 - I don't know where particular components are and which ones usually cause problems in that unit. My suggestion was aimed at CRT monitors in general. Hopefully someone who knows the VT100 better will reply with more specific suggestions. If you are getting multi-kilovolt arcing, I expect you would be hearing loud, sharp, cracking noises. I think what you need to look for is more of a very soft purple/blue corona discharge which is hard to spot and probably makes little or no noise. As I don't know the layout of the VT100, it is hard for me to suggest places to look for this other than in very general terms. It could be something like a pinhole in the EHT cable, EHT connector, flyback transformer etc allowing a corona discharge to something nearby that happens to be at a lower potential (which is everything where EHT is concerned). Maybe the plastic / rubber etc insulation of some of these components is breaking down and getting soft? Switch off and wait long enough for everthing to discharge before checking for this sort of stuff with bare fingers. If there is muck / grime / soot on the glass of the tube around the CRT final anode connector, this could be part of the problem. If you try cleaning this off, don't clean off the dark grey / black aquadag coating which is supposed to be there. There will be a gap in the aquadag around the final anode connector where there should just be clear glass. Best to clean with isopropyl alcohol or something similar that will evapourate completely afterwards. Whatever you use, make sure everthing EHT related is fully dry before switching on again. Similarly with muck around the connections to the flyback transformer. If the terminal has been stored in damp conditions, you could be getting internal discharge in the flyback transformer. If you suspect this is the case, someone more familiar with the VT100 may be able to advise how to get the flyback transformer dried out. I think it's unlikely on a small monitor like the VT100 but it might also be worth looking at the scan coils. If there are spark gaps across some of the connections to the tube base, either on the main PCB or on the tube base panel, if there is one, it may be worth peering at those looking for corona discharge. Again, I think this is unlikely on a small monitor though. Someone more familiar with the VT100 may be able to advise if it is safe to disconnect the tube heaters in order to get more darkness to look for corona discharge or if this would be likely do damage to anything. You could turn down the brightness so that there is less stray light from the screen. One more thing, give your eyes time to get accustomed to the darkness when checking for corona discharge. Be careful not to accidentally get too close to the EHT components in the dark though. The diagonal lines may be unrelated, again someone more familiar with the VT100 would have to comment. Regards, Peter Coghlan.

Peter If you are still listening through the "on topic" noise - see below Martin I don't have a laid apart flyback transformer, but I could provide a VT220 of the YMMV kind. I'm in Dorset, UK, please reply off list. Best Regards Martin