Sony Trinitron KV-EX34M39 has OSD and sound, but a low contrast image output

[brik]

Hey all. I received a Trinitron for the purposes of retro gaming, but it has a really weird issue. When you first turn it on, the image will be fine. But after about 15-minutes, it will go super low contrast and no amount of fiddling with the settings will it bring it back to normal. However, the on-screen menus, text (channel number, etc) all display no problem. Additionally, the sound works too. I should add that I've tried a few different input sources, and they all act the same.

I did a bit of Googling around, but the only indication I found of a fix was adjusting a "screen" knob that is found when the back it removed. I tried turning it a few different ways, but the problem persists. Here is my source for that fix: http://www.pechorin.com/m/2008/03/16...en-316314.html

If it helps, here is the service manual: https://www.manualslib.com/manual/83...uct-KV-EX34M39

And a few photos of the problem: https://imgur.com/a/lphgWnG

Cheers in advance!