20 Dec
2022
20 Dec
'22
10:18 p.m.
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
<cctalk(a)classiccmp.org> 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(a)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!
>