[volt-nuts] VFD wearout (was "dark display for 3458)

[Didier Juges]

After the thread about the 3458 display, I went back to one of those VFD
that I mentioned in my earlier post. These had been used with only a few
digits turned on on the first line, the rest of the display being normally
turned off and only used occasionally. After several years of continuous
operation, the digits that were used  had lost brightness and more
interestingly, the other digits had also lost brightness but also looked
botched (the brightness was very uneven).

It turns out I have been using one of these old displays on a new project
(it's a development job, so the unevenness does not bother me at the moment
since this display will not ship). After about 2 weeks of continuous use
where most of the digits are used, the display is now just about back to
normal. somewhat dimmer than a new one, but the unevenness has completely
disappeared.

It looks like either the digits themselves, or the cathode wire, had become
contaminated as a result of not being used, and a few days of operation
restored their activity.

Even more interesting, at the moment, I cannot detect a difference in
brightness between the old digits that were on for several years and those
that were not. The display is generally dimmer than a new one, but the new
ones are a different part number, the original device having been
discontinued, so it may also be that the new display is brighter because of
process improvements by the manufacturer (something the manufacturer
advertised when they introduced the new device).

On this development job, most of the digits are used, and the display is
constantly changing (scrolling messages).

Anyhow, I thought it would be interesting to mention.

Didier KO4BB