Sony PVM 20M4E Only Displays Picture / Menu when Underscan Button is Pressed

[pvmhelp]

I have a Sony PVM 20M4E that only displays the picture / menu when in underscan mode. If I take it out of U/S mode, I just get a blank screen (Menu doesn't work) brightness / contrast controls don't work.

I'm hoping that that is enough of a clue to help me narrow down the issue. (Definitely rules out the PSU, Neckboard and Input Board at the very least).

I've been testing capacitors and found two which were out of spec in the defection area (as far as I can tell). They were both adjacent to heatsinks. I replaced them thinking that that would solve the issue.

I put it all back together and it has made no difference at all.

So I guess I'm back to testing the remaining caps and reflowing every joint).

It's a lovely burn free, sharp tube. I'd love to get this going again.

Any pointers would be greatly appreciated!

Service manual: https://archive.org/details/SonyPVM20M220M4ServiceManual

[m k]

The machine is not generating any pictures.
OSD menu is piggypacking what is coming it.

So underscan picture goes thru, but normal size is cut out somewhere.
Start following U/S signal, it's either on or off.
Maybe it is partially faulty and not selecting everything it should.