X68000 Monitor Brightness Issue

[Pinwizkid]

Need some help from the x68000 monitor gurus out there... If you exist! My X68000 monitor is inconsistently displaying brightness between 31 khz and 15 khz. I recorded a video to explain it better. Also, if it matters, 24khz mode behaves the same as 15khz. Model of monitor is a CZ-612D. Thanks for any help or tips in advance!

https://youtu.be/HVSrjUGO4d8

[kamiboy]

Cold solder join would be my best guess. Had a sporadically fluctuated brightness problem with one, managed to solve it by shotgun reflowing all joints on the board where light tapping had the biggest effect