How to adjust the DEC VR201 monitor, aka Rainbow monochrome monitor

    This is the text of a message that I posted on the DEC PC Forum 
some time ago explaining how to adjust the Rainbow monitor.

         -- Carl Neiburger, 72336,2257


     DEC's design regretably requires you to open the monitor case to get at 
the controls.  And, given that it's often necessary to do so, that design is 
dumb, dumb, DUMB.
     Getting inside the case is not too difficult, fortunately, though it is a
nuisance.  Furthermore, you have to be careful in opening the case, because
the monitor retains a substantial electrical charge even when it is unplugged,
which poses a shock hazard.  But it is possible to work safely.
     First, make a good table space that will allow you to lay the monitor
picture-side down while you open the case and then roll it back on its
haunches when the case is opened up.  If you do it that way, then you'll only
have to touch the plastic frame around the picture side, and you won't risk
getting shocked.
     First, disconnect all the wires at the back and extend the plastic foot
on the bottom of the monitor as far out as it will go.  This is important,
because, if the foot projects into the monitor case, it will strike wires
inside; you won't be able to open the case and may damage the monitor.
     Now, put the monitor picture-side down, making sure that the foot doesn't
flop back inside. In the center of the back, there's a round, white, plastic
cap that you can pry off. Unscrew the screw beneath it, and you should be able
to lift off the back.  Now, you can reconnect the cables (so you can see
what's happening when you make the adjustments) and carefully hold the monitor
by the plastic in front as you roll it back into position.
     A roughly trapezoid circuit board is on the top of the monitor, and the
"trim pots" for screen adjustment are mounted on the left and right sides of
this.  Adjust these with an electrical screw driver -- preferably with a
plastic shaft lining -- to avoid shock.  Don't touch the pots directly.
     If you're lucky, a piece of paper on the monitor will label the pots. On
the left side, reading from back to front, they are vertical hold (VH), height
(H) vertical linearity (VL), horizontal hold (HH) and horizontal center (PH).
     On the right, reading from front to back, the width coil (not a pot but
an ajustable coil, is near the front, and the focus and cutoff pots are
together near the back of the tube.
     I think the only ones that need explanation are vertical linearity, which
is used along with the height control; apparently it is used to compensate for
distortion that can be introduced in adjusting height; both adjustments may
also affect the vertical hold.  The same kind of three-way relationship exists
between the horizontal center, width coil and horizontal hold.
    The cutoff control determines the strength of the electric signal needed
to display stuff on the screen. If the signal is set too low, the screen goes
blank.  DEC doesn't provide any useful information in adjusting it in the
material that I have.