Odds are the dim pix is all 3 CRT's are weak. You can test them with
a universal adapter on a Sencore etc. The G-2 setting may be different than the usual 50V. An adapter can be made up for any checker if you have the
schematic for the checker & pin out for the CRT.
Aside from that you can check the CRT voltages. educated guessing is cathodes 125-150V ( the higher the dimmer ), G-1 0-50V, G-2 400V. For focus the
controls should focus best apx mid range. I never measured HV so have no idea. A normal chassis with a tripler gives 25-32 KV but these may run less.
If nothing else you have a piece of TV history. These were the first big screen
projo's to sell VERY well & lead to all the ones to come.
73 Zeno
LFOD !