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Vacuum Fluorescent Display Missing Characters
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Pootle:
I have a synth with a vacuum fluorescent display and it is missing some characters. I wondered whether anyone had any experience of this phenomenon and knew whether it was likely a fault with the VFD itself, the controller chips or the connections. No schematics are available, so I don't want to start getting deeply involved if it is probably the VFD itself and therefore presumably not repairable.

Any insight would be great.

floobydust:
It's not the VFD, with so many digits missing I would go after the IC's doing the digit-drive to the VFD's grids. One IC could do say 6-8 and that IC would be suspect. You'd have to post pics of what ICs are used.

edit: a synth gets banged around a lot, so look at the VFD's soldering for fractured joints, although I would expect other problems like missing segments then.
james_s:
It's possible that it's inside the VFD, for example broken connections to some of the grids, but I agree it's more likely to be external to the display itself.
Benta:
The ICs are unlikely. But the pin-to-glass connection points on the display can be problematic, and are very difficult to repair.
floobydust:
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.
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