Fairchild 777 dualbeam scopen info

[PA4TIM]

I'm restoring a Dumont/Fairchild 777 4 plugin, dual beam 100 MHz scope from the late 60's.
I found manuals for some of the plugins but not for the psu / display unit ( or mainframe as you like)
It looks a bit like a solid state version of the Tek 556, it is allmost as big but then modtly silicium and nuvistors.

The PSU looks like the one in a 766 but this one has three adjustments the 766 does not have. -50, +50 and +100 balans. And I have no clue how to adjust them and their purpose.

Problems found now is a few totally dead filter caps ( electrode ripture) and as a result no stable -50V Vref and a huge ripple.
One vertical plugin is dead. No respons on vertical position, beamfinder or input but that should be rather easy to fixbecause i have the manual from that plugin.

Does anyone has info ?

[PA4TIM]

Is this scope realy so rare that no one knows it ?