OP, I forgot to say welcome to the forums, and note there will be conflicting opinions all the time. It's part of the fun.
Blaming the VFD or CRT is common and yet not always the problem. It's best to use troubleshooting technique to find out what the problem is, but with no service manual that takes tremendous skill. What make/model is it?
Keyboards I've repaired are plagued with fractured soldering joints. I'll first spend 1/2 hour with a magnifier and soldering iron doing touch ups. The jacks and keyboard, buttons are common places. I would look at the display and driver IC soldering.
VFD construction, mechanical failure it's not feasible to have a group of digits stay off so I suspect a driver IC or power to it. A disconnected grid leaves a digit lit, as vacuum tubes are normally on devices, they need -ve bias to turn off.