Hello yaaku,
I'd say with high certainty you have a thermal problem, where a component is changing its value
with heat.
Brian's suggestion would be the first thing you need to do. Failing that, then you need to
get the aid of a can of freeze spray to isolate the offending component.
Failing using freezer spray, you can easily swap components from the red drive with the green one.
You should eventually find the culprit.
Try concentrating on equal value electrolytic capacitors, signal diodes, transistors and resistors.
You should find that each gun will have their own independent but identical valued components,
as this will make it much easier.
If you find no faulty components on the CRT PCB, then you need to trace back to the chroma
processing. Best thing is to get a datasheet of the chroma IC to give you an idea of the section
on your main PCB where you need to tackle the fault.
This is not a common fault with the other colours which will make trouble-shooting the fault a
hell of a lot easier, therefore you need to look at identical parts for each of the components
that share identical values.
Please let us know how you get on.
Regards,
Relayer