2 Dec
2013
2 Dec
'13
1:58 p.m.
This unit also has a totally different video monitor
circuit than the
older ones and my problem lies somewhere on that board-- I am getting
a very dim image even though the CRT itself appears to be in very good
I know nothing aobut this VT220, but I';ve worked on plenty of CRT-based
monitors....
My first question is : 'Is the picture approximately normal size (even
though it's dim) or is it much too large?'
The point being that if the EHT (HV, fianl andoe votlage) is low, the
picture will be dim, but it will also be large. The slower electrons are
easier to deflect (to put it over-simply).
If the picutre is abotu right for size, I would suspect one of the other
votlages. Maybe first anode (g2 to you). Maybe the control grid. You
could try comparing the CRT pin voltages with those in a workint unit to
see if one is way off.
I suppose it could be a low-emission CRT.
A 'silly' whihc I will admit caught me once, is a very dirty screen. Yes,
I spent a long time goign trhough the video PCB in a VT100 trying to find
a fault when the reason for a dim siplay was the screen was caked in dirt.
-tony