In my years of servicing PC, I often encountered problems on CRT monitors that is cause by a cold sorder(usually from CRT and vertical circuitry).When CRT module or a particular component heats up over time, it will tend to loosen up its solder and later will cause intermittent problem on your monitor display.
You will know if your monitor is experiencing a cold solder condition if you have an intermittent display problem(disappear or re-appear when its external casing is tap or shaken).Discoloration of display can be also cause by a solder joint.
Cold solder joints is easily recognize by carefully looking its individual solder in the circuit board,normally good solder looks smooth and firmly secured on the PCB, while cold solder joints show some cracks and solder is rough.
Once you suspect or identify a cold solder joint(s), try to remove and clean first the existing solder before re-applying a new solder,in this case it will ensure a good solder contact between component and the circuit board. Others just re-heat a particular joints without cleaning its previous solder, find the problem to re-appear later.
Most cold solder cases appears on class B monitors,if you dont want to experience less cold solder problems on your CRT monitor, I suggest buying class A monitors(LG,Viewsonic,Samsung,HP...etc).
Tools needed to repair a cold solder joints:
30 or 40 watts soldering iron