[cctalk] Re: unpleasant odor from VT100
Peter If you are still listening through the "on topic" noise - see below Martin >>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 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
[cctalk] Re: unpleasant odor from VT100
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, 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@classiccmp.org> wrote: > >> 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! >>
[cctalk] Re: unpleasant odor from VT100
Hi Hush: There are dangerous - potentially lethal - voltages inside a CRT display, so be very, very careful if you don’t have lots of experience with these devices. Touch the high voltage points by mistake and you are likely dead on the spot. The issue probably relates to bad electrolytic capacitors in the high voltage circuitry, or with the flyback transformer as another reader has commented. Best course of action as it doesn’t sound like you have a ton of high voltage servicing experience with these devices is to visit an old school TV repair shop. Techs there can probably figure out what the issue is. Schematics are available for VT terminals on bitsavers and similar sites. Not to be alarmist, but BE CAREFUL! Kevin Sent from my iPhone > On Dec 20, 2022, at 14:06, hush hush via cctalk wrote: > > 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@classiccmp.org> wrote: >> >> 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! >>
[cctalk] Re: unpleasant odor from VT100
Might've just been a dead bug that got cooked. Check for a carcass. Sellam On Tue, Dec 20, 2022 at 2:06 PM hush hush via cctalk wrote: > 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@classiccmp.org> wrote: > > > 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! > > >
[cctalk] Re: unpleasant odor from VT100
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@classiccmp.org> wrote: > 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! >
[cctalk] Re: unpleasant odor from VT100
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!
