"frank" wrote in message
...
isw wrote:
In article , frank
wrote:

If the filament were made up of two parts in parallel, and one of the
parts failed open, could that account for both the dimness and the
overheating 555?

the filament has two wires that run for all the display length. However
I can't tell if these two wires are in parallel or in series electrically.
Supposing that the two wires are in parallel, then since they run
for all the display length, it shouldn't make any difference on only
the rightmost digits. One open wire would also mean higher resistance
so probably the 555 would run cooler too.


Take the thing into a dark room; often you can see a dim glow from the
filament. Do you see it over all parts of the display, or only over the
"normal" part?

I'll try to verify this, just for the sake of it.

Frank


I dunno - I've seen many VFD's that simply were aged and had similar
problems.

Replacement was the fix. Increasing the filament voltage might help, but I
suspect the dimmer segments still won't be as good.

I once fed about 60 volts to a nominal 5 volt filament before it failed, so
I don't think they are terribly fragile.


Mark Z.