8 Oct
2007
8 Oct
'07
2:58 p.m.
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.
Yes and no. They are magnetically focused CRTs as the model number
implies; it's an MW type (Mxx-yyW) made by Philips, an
electrostatically focused CRT would be an AW-type. And there are four rings on the neck arranged in two pairs. One pair (the
one near the
deflection coils) controls the centering, and the other pair (towards the
beam system near the socket) controls the focus. But additionally the
To do magneitc focussing, you meed a pretty strong magnetic field running
along the axis of the CRT. I doubt you'd get that from a couple of
magnetic rings.
focus is fine tuned with a potentiometer on the video
board. BWT the focus
and centering rings are described in the VT100 technical manual.
I think that most high quality CRT systems like monitors are magnetically
focused; I've seen such CRTs several times in video monitors and
terminals.
I;ve never seen one. OK, most of my high-end monitors are colour, and you
don't try magnetic focussing on a colour CRT (there's enough prolems
getting the convergence and purity right!), but nonoe of the monochrome
monitor service manuals I've read mention magnetic focussing. I've never
seen a yoke with anything other than centering rings on it.
other than the VT100, can you give me a definite pointer to a
terminal/monitor service manual that uses magneitc focussing?
-tony