I have an issue on an Apple IIgs RGB monitor (A2M6014), which I recently got.
The problem is: it works well at initial power on, but after some time, the screen starts flickering and collapsing vertically, and then eventually it collapses to a horizontal band (or even to a line). The 10-second video below shows the symptom.
I found some information from the forum, although I don't have expertise at all --- I've found the schematics of the monitor, and I learned that it might be a "vertical deflection" problem, which could be caused by cold solder joints on the "HV module (flyback)". So I resoldered all the pins of the HV module (luckily I knew how to solder), but it didn't fix the problem.
What should be the next step to repair it? Any comments will be greatly appreciated!