Degradation of old Fluorescent Displays?


I just found a "UniCom 1216" calculator for $1.50 . It's a bit larger than an HP-97, no printer, and basic four-banger business adding machine functionality. (Everything seems to work fine.)

The display is an orange fluorescent (I think) 12-digit unit. I notice that the higher-order digits all look nice and crisp, with each segment clearly dilineated with razor-sharp borders.

As I look toward the digits to the right, they get progressively less well-formed. Most the lower five digits' segments each have a "blob" of orange hanging off of one side or end -- it's as if something has "bled" out of its original confinement.

The problem seems to be worse on the most-used segments (keyed digits enter from the right). Also, some of the segments on the rightmost two digits are dimmed.

Is this a common problem with fluorescent displays, and is it, in fact, related to frequency and/or total duration of use?

I don't expect anything can be done about it -- I'm just curious.


The display you describe is likely a Burroughs PanaPlex-II, which is a neon display. The problem you describe is fairly common on older PanaPlex displays that have seen a lot of usage. I'm not sure the exact cause, but I've seen a lot of them and believe it is just due to time of use. The best example is one of the Garrett combo calculator/clock displays I've seen, where the clock digits stayed on all the time and are worn out, but the other digits are still fine. There is no fix I'm aware of other than to replace with a newer PanaPlex display. Alex Knight


i had an orange screened ti calc that was also a clock and the digits that displayed the time had bled into the surrounding area while the others remained crisp.



You are right - you had...

In the meantime this TI-3510 arrived and I took some pictures of the display. It really faded away.

View it yourself here:

Click on the small thumbnails and you get a huge picture of the Panaplex II didgits.



J - it's better off at your house than mine; i never used it. the enter key was missing. - d


I wonder if the voltage that the display is fed is critical? Or whether it's AC or DC?

I have a Heathkit digital clock which I built in the mid-60's (!) and the display looks very similar to those in the reference given by Joerg Woerner. However, my display is still nearly perfect after almost 40 years of continuous use.

At the moment, the clock is at another location, so I can't go look at it to figure out exactly what the display is made from. I think it is miniature neon tubes of some sort (but definitely not nixies). Is that different from what's being discussed here? (Neon lights are not "fluorescent.") What voltage did these calculators/clocks run from? 110 VAC wall power or low voltage batteries? Joerg's unit labels it 120 volts - like the Heathkit.


This site suggests they're called "Vacuum Fluorescent Displays" (VFD) and are still used, generally in AC- (line) powered devices. The module in the UniCom 1216 appears to be what the site's author calls a "third-generation VFD" -- with a digit assembly sandwiched between two pieces of glass.

Certainly the orange glow looks like that in the little "neon" lamps that are often used for indicating "power on" in coffee makers and ranges.

. . . and, other than being orange rather than red, the deterioration in the most-used digits looks exactly as that pictured at Joerg Woerner's link (above).

Thanks for the responses . . .

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