First off is that the chassis on 2 big boards side by side ??
If so there is a NP 'lytic cap in one of the power supplies (run)
that HAS to be changed. ( a chassis pix would help). It opens
& creates all kinds of havoc.
Besides that for now be sure you can turn the brite ALL the way down
with the customer control. If not look at the G-2 voltage and the
200 V (apx) source that runs the 3 video outputs on the CRT sockets.
Screen shots of real content may help us also.
73 Zeno
LFOD !