VT101 screen adjustment

tony duell ard at p850ug1.demon.co.uk
Tue May 10 10:10:28 CDT 2016

[VT101 with vertical linearity problems]

> Yes indeed. Fortunately this one wielded under my trimmer and all is
> properly aligned now. All I need to do now is troubleshoot the keyboard
> circuit which I hope is the same as the VT102...

In general it is a bad idea to cure faults by adjustments. Unless somebody
has been twiddling, these adjustments only drift if some other component is
failing. They are there to initially set the circuit up for the components that
are used, or in some cases, particularly in delta-gun colour CRTs, to correct
for external conditions, such as magnetic fields.

My guess is a capacitor is failing. So far you are still within the range of the
adjusment, but it may well get worse. I don't know which video board you
have (there are at least 3 different ones), but if it's the one on pages 54-58
of the VT100 printset on bitsavers (the VT100 and VT101 use the same 
video board), then check C318 and C319 for a start.


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