Monitor suddenly become discolored

VERY discolored monitor

Okay, I showed this to the guys at KLOV (great suggestion, discgolfer... and they said to adjust the yoke back and forth. WONDERFUL IDEA! What the hell does that mean? How do I DO that?

There it is. What to I do, anyone? What parts should I NOT touch?

This sounds scary, and it is, in two ways.

#1
That fat red cable in  your photo is the anode wire, you definately don't want to pull/touch/play with that while the monitor is on. (There is high voltage on it that can kill you.) (see monitor discharging 101 on internet..)

#2
The yoke is the whole thing sitting on the neck (thin part) of the tube..
If you manage to break the neck of the tube trying to get the yoke off, it would implode, sending shards of glass into your body.

The reasoning   behind the discolouring is sound though.
The yoke (thin copper wiring under the black tape) controls where the beams hit your tube. It's like a magnifying glass, and could be out of focus in the center, causing too much of a certain 'colour' beams to hit the center, which in turn causes the effect your seeing.

If you do manage  to loose the yoke, you would need someone to watch the front of the tube as you adjust it, then use the small pegs+glue to keep it in place. A really tedious job..

The yoke is adjusted in the factory normally to have correct output. You can see those small pegs wedged between the yoke and tube, those are glued on so that the yoke stays in place. Perhaps one of those pegs fell out ?

This picture explains more clearly:

- Black things on top of neck: convergence adjustment (under white (tape?) on your tube)
- Metal strip+screw: holds yoke in place
- Copper wires: yoke coil part (this they want you to move up/down the neck.)
- Pegs+glue: factory adjustment to keep coil centered/in place etc.

Basically these are the steps:

• - Remove neck board (pcb)
  - Unscrew the part that holds yoke coil in place (metal strip+screw)
  - Move yoke coil away from the tube a bit
  - Re-screw
  - Ensure pegs keep coil in place.
  - Re plug neck board. check picture. etc.

If you have no experience with this, i suggest another monitor.. there are people that go and move around the whole yoke assy from one tube to another for a living, but it's a potential dangerous thing to attempt if you've never done it before.

undo the yoke clamp screw and seperate from the glued wedges between the yoke and CRT. If you are not sure what you are doing you are likely to end up with a worse purity error. If may even be the CRT itself faulty.

Tip- ground the red cathode  via a 4.7 K resistor (not critical), that will give you an all red screen to play with. The problem with shifting the yoke is that it does not only adjust purity but convergence as well.

Edit-Asure, the pic you  posted is of an older gen CRT with adjustable convergence and purity magnetic rings. Spikes is later gen without those physical adjustments.