Shagittarius wrote on 2022-07-27, 18:24:
Sorry, Not having an easy time finding a manual or any info about a similar problem, the fade out is pretty common but that zoom is weird.
There is a plausible hardware failure that would explain this behaviour: Failure of the anode voltage insulation. A color monitor like that typically generates a high voltage of around 25'000 to 30'000 volts to accelerate the electrons that hit the screen and cause it to light up. That voltage is generated inside the line output transformer (also known as flyback transformer), and transferred through a wire with very thick insulation (oftentimes red, sometimes black) to the picture tube, with a connector protectected by an insulating suction cap. If that voltage goes down, the electrons are not that fast when they hit the screen, so the picture gets darker. Also they are already too slow while they are in the deflecting magnetic field, so the field influences them for more time and they get deflected further, this would be the picture zoom effect. As it happens gradually, I suspect some component starts to leak high voltage when it warms up. My first guess would be one of the couple of high-voltage rectification diodes that are part of the high voltage transformer. If that diagnosis is right, the line-output transformer has failed. Repairing line-output transformers is typically impossible because it is very difficult to keep it properly isolated to handle the high voltage, and it is most likely potted anyway for extra insulation. Replacing the transformer might be an option if one is able to source a suitable replacement. Typically, a failed line output transformer means repair is not economically sensible, I'm afraid.