keenmaster486 wrote on 2023-07-12, 04:36:

After the monitor is on for 10 minutes or so, a splotch of slight yellow tint appears on the right hand side of the screen, and the left hand side of the screen turns slightly blue. I cannot tell if the built-in degausser is even working at all, though.

This sounds like capacitors but I have horrible visions passing through my mind of a shadow mask that slightly warps when it heats up or something like that.

To be honest, I have no idea how bad capacitors can cause an issue like that, especially on an old monitor that has no electronic purity correction. Color purity on these CRTs on adjusted purely by the magnets on the rings glued at the neck of the CRT. Heat will slightly warp the shadow mask when it warms up - but if the monitor is in proper condition, it should not warp the shadow mask that much that color purity is significantly affected.

Thinking about the degausser is a good idea! If the shadow mask is magnetized, this wil interact with the color purity adjustment. A slightly magnetized mask may have the effect you describe. While the magnetization doesn't explain why the symptom manifests only when the CRT is warm, the purity issues might only occur of both heat-related warping an magnetization occur at the same time. Checking the degausser is actually quite easy: When you power up the monitor (after it was powered off for at least 10 minutes), it should make a kissing-like sound. If that doesn't happen, degaussing very likely is broken. Most of the time, the PTC that controls degaussing has failed open in that case. You can confirm this effect using a meter, too: With the power switch turned on, the resistance between live and neutral is expected to be below 20 ohms: As long as the PTC is cold, it's resistance is around 5 to 10 ohms, and it is in series with the degaussing coil, which also has a very low resistance.

8513 ages badly due to awful CRT quality, and another possibility the CRT shadow mask was knocked out of alignment.

Shadow mask with frame is designed to be snapped into glass pegs with electrical connection to HV or ground, I forgot, on front glass plate, this was removed and installed several times as they photo developed the triad of RGB phosphors one by one.

Each shadow mask frame is sightly different from another due to manufacturing tolerances so each CRT is paired with same shadow mask throughout the manufacturing to keep the alignment.

Cheers,

keenmaster486 wrote on 2023-07-12, 04:36:

...but I have horrible visions passing through my mind of a shadow mask that slightly warps when it heats up or something like that.

That is exactly what this sounds like 🤣. Whenever there's discoloration on the sides that seems to also correspond to image brightness it is the mask warping from heat produced in these parts with higher beam currents. A good kinescope uses a mask made out of invar which warps way less and it takes a solid white screen to make the problem appear but this is mostly a large screen issue and not a monitor sized stuff one...

Degauss issue that has been described earlier can be plausible, if it doesn't function these sort of problems can definitely happen. Lot of early and cheap monitors keep the PTC always hot and they simply burn out over time. Better monitors use a relay to disengage the PTC after degauss time has completed, sparing the part from being cooked and it also can improve image, on all monitors and TVs that I have seen that keep the PTC always on there's avery slight 50/60Hz wobble on the screen. I always mod these things to turn the PTC off after say 10 seconds and this becomes a nonissue and the part also lives a much longer time then.