7 Oct
2007
7 Oct
'07
1:42 p.m.
Oh, and questions concerning another VT100: What may
cause a bad geometry
of the picture on a VT100 (slight trapezoid and pincushion; Philips CRT)?
Are the sloping sides of the trapezium horizontal or vertical?
Trapezium problems can be caused by the deflection yoke, of course
(shorted turns or other prolems in one coil of the pair), but before
worrying about that, I'd make sure none of the supply lines on the video
board have a sigificant ripple at one of the scan frequencies.
The only adjustable magnets are the two sets of rings
on the neck, one for
the position and one for the focus (it's a magnetically focused CRT as
most monitors are).
Every VT100 I've worked on -- in fact every monitor of any type that I've
worked on, has been electrostatically-focused. There's a preset on the
video board that adjusts the votlage on one of the CRT pins (I forget if
it's pin 6 or pin 7). The 2 rings on the back of the yoke are both for
picture positioning.
-tony