On 9/7/2016 3:38 AM, frank wrote:
Hi all,
has anyone ever seen a VFD (vacuum fluorescent display) failure in which half
the display is very dim and the other half looks good?
I have this 16 character (16 segments) 1 row display and the first 8-10
characters have a normal brightness, the rightmost ones are very dim, barely
readable.
I first suspected a problem with the filament supply, but swapping the
filament pins has no effect, so I'm a bit puzzled.
Waveforms look identical on all the 16 grids too.
Unfortunately I have no schematic of this instrument (digelec 824 eeprom
programmer), nobody else in the world seems to have this programmer also,
so I could not ask anyone for some quick waveform comparison.
I'm starting to suspect a bad VFD but I can't imagine how would it fail
like this.
Part of the filament supply is made with a NE555 that's getting quite hot
and also a 120 ohm 1/4W resistor near it gets too hot to touch, but all
components I could test looks ok. I swapped the 555 and it doesn't make
any change. If I leave the 555 out, the display has no filament supply.
Any hint is really welcome.
Regards

Frank IZ8DWF

Hello all,

I've seen several VFD's that have this issue, usually on the segments
that are rarely turned on, like a 12 digit calculator. One temporary
fix is to type in a ll "8" on the display, to light the greatest number
of segments and let it burn in that way for 24 hours. That usually
fixes the problem for a few months.

Regards,
Tim
Bristol Electronics

P.S. One amplifier manufacturer I deal with and had problems with their
display issues a new software revision that had a "light everything on
the display" function which they instructed you to leave on for 24
hours, and it did work. I think contamination plates rarely used segments.