Like anything else - I would start by ruling out more fixable items such as the power supply. Low voltage on the supply? Simply replacing caps and diodes doesn't mean a fully functioning supply.

Hard to say without seeing schematics on that specific version.

There is usually a filament voltage in addition to cathode and anode voltages. Without any form of schematics, tough to say if any are missing. But based on photo in first post - I would check the filament voltage. Now what that voltage is and where to find it is particular to the specific display on that board -- impossible to define without schematics or further information.