Magnetic shielding for monitor ?

[Level42]

In my Play Scene Jamma cab, the games PCB's used to be on a drawer that is sliding in tilted towards the back of the cab. Since it was so idealy suited, I used it to place my PC parts on this "drawer" board. However sometimes, especialy with bright (white) parts of the screen I can see there is discolorisation, very much like when a CRT needs degaussing (or a magnet is near the CRT).

The spot is near the place where the Power Supply is, but also near where the cooling fan of the CPU is. Since the Power Supply is in it's regular metal shielding I wonder if this is the cause or the fan. What do you guys think, and is there a (simple) way to shield off the CRT completely ?

[grantspain]

i had a similar problem on a lost world where i changed the rptv,the only way to rectify this problem was to move the magnetic source which was the transformer,i assume  your psu would cause a similar problem as this, so maybe just moving your psu would suffice.fans can cause a similar issue more so if they are mains input.