I have an iMac G3 from the Summer of 2001, and it appears to have an issue with its CRT.
After a few minutes of being on, the entire CRT appears to take a yellowish tint which is extremely visible, especially on blue and white colours.
I decided to go into display settings and colour calibration and turn down each RGB channel individually, and I found turning the blue channel down fully reproduces this yellow tint, and I therefore assume the blue gun is not firing fully or at all in some cases. Is there any way this can be fixed and any reason this may occur? I really do not want to replace this machine as it was a Christmas gift as my family knows I collect these older machines.
Best Answer
I doubt it's the gun that's the issue, but without getting actual hands-on, it's impossible to tell for sure.
It could be something as simple as color being out of sync and a simple degauss should correct. Pass a magnet across the front of the screen; that should clear things up. You don't need anything powerful. I've used re-purposed speaker magnets back in the day. I have also seen people use tool magnetizers with the added benefit that if it doesn't work, you still have a functional tool for future magnetizing needs (from $2 to $10 USD).
If the degauss fails, it may be a component or a faulty solder joint that controls the color hue/saturation. At this point, it would be best to take it to a pro who specializes in this type of diagnostic/repair. It's not a difficult repair and shouldn't be costly at all. It's just that you will be working with extremely high voltages and can be quite dangerous for the novice.