Bright spot in center of G4 iMac LCD

[Quadraman]

What would cause a bright spot about 2-3" across in the center of a G4 iMac LCD screen? The screen is still usable, just the center is brighter than the rest of the screen.

 

[wally]

Well, as a speculation, a temperature variation. In the Sharp Application Note on Mechanical Design Considerations for LCD Displays, "It is important to note that variations in temperature of as little as 5 degrees centigrade can cause an apparent non-uniformity in the contrast of the display." In the case of the all in one iMac the heat conducted by the support pillar and the centrally reinforced construction of the LCD rear shell may result in a different central area temperature as compared with the rest of the air cooled LCD. Today I saw a gutted, scrap iMac at a surplus store, just the empty hemisphere base, the hinged pillar and the LCD mounting backshell with dangling display connections (minus the display). There is a reinforced area about 2.75 inches in diameter on the backshell where the mechanical stess is maximum. Also, this is where the display and wifi antenna cables enter. Unless the LCD is installed with enough heat spreading metal layers in back it might see a different backshell temperature right at the center rear. Check that the base unit cooling is adequate.

 

[~Coxy]

The Rev A AlBook 15" models had the same problem due to pressure on certain sections of the LCD during shipping.

I would hazard a guess that at some time the iMac had undue pressure on the LCD. Due to the position of the mounting neck, it developed that white spot.