"Tim Schwartz" wrote in message
...
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.




Interesting. I don't think this would help with some dot-matrix type VFD's
like the newer Yamaha's, where a few I've seen will light every other row
unevenly, or like a heavily used Fluke 8840 with each segment lit more in
it's middle and dimmer at each edge, but seeing as how Yamaha has a "light
all" option in their diagnostic menu I plan to keep your post here for
posterity. Might come in handy (or not - I'm retiring soon; don't know how
much I'm going to be doing audio in the future)

:-(

Mark Z.