LCD displays life expectancy


For how much longer should we expect LCD displays of HP-41s to function properly?


Remembering documents from the mid-80's when the 41 was in its heyday, the biggest enemy to LCDs is not feeding them properly, giving them a net DC so they plate up on one side. Assuming HP designed their circuitry right, that's not a concern. The next enemy is heat and humidity, especially the combination; but Hantronix' website says the life expectancy of the LCD glass is 50,000 hours of use (almost 6 years of never being turned off), and I had a battery-powered LCD clock in the car for that many years and it didn't seem to deteriorate at all. (The mechanical clock had quit working so I stuck a $2 LCD clock from the drug store over it.) UV isn't good for them either, but I doubt that you leave your 41 in the sun. I have seen an LCD that was damaged by extreme heat or UV and the silver background had turned very dark blue IIRC. My own 41's LCD looks the same as it did new 23 years ago, with the bright silver background and really black segments. I really don't think you have anything to worry about. LEDs OTOH have a half life.


I have seen lots of failed "early" LCD displays:

- ca. 1972/1973 Rockwell LCD: almost 100% chance of being dead

- ca. 1973/1975 Sharp COS: 50% of being dead

- ca. 1976/1977 LCD (with or with yellow filter): 25% of being dead, sharply rising as of lately, still a 30 year life span

- later LCD: almost 0% being dead

This is of course only valid if you don't expose the display to intense sunlight or heat for longer period or physical damage.

There are several other parts of the calculator that will fail before the LCD.


I have seen lots of failed "early" LCD displays:

- ca. 1972/1973 Rockwell LCD: almost 100% chance of being dead

- ca. 1973/1975 Sharp COS: 50% of being dead

- ca. 1976/1977 LCD (with or with yellow filter): 25% of being dead, sharply rising as of lately, still a 30 year life span

- later LCD: almost 0% being dead

This may explain why HP introduced an LED-display line (Spice series) in 1978, just before the upscale LCD HP-41C in 1979: They wanted to ensure that LCD technology was mature and reliable.

My much-cheaper Casio fx-3600P (bought in 1981) replaced an LED-display TI-30 from 1977. The Casio's LCD has had no problems, although I have used it very sparingly since I bought an HP-15C in 1983. That year, the still-available LED-display HP-34C with rechargeable battery looked retro by comparison (a "super TI-30"!), but I still gave it serious consideration.

-- KS

Edited: 6 Oct 2009, 11:32 p.m.


... allow contrast adjustment 8^) If the LCD begins to fade out, just 'push them up' a little bit.


Luiz (Brazil)


How? I know I have read it somewhere, but since you brought it up please save me a few minutes of research.


BTW, I use my fullnut over my halfnut just for the contrast of the fullnut.


easiest is using the sandbox or the hepax, both of which have contrast and ct+/ct- (or similar commands. Do a CAT 2 and it will pop out immediately) to request, set, increase, decrease contrast.





Thanks. It is persistent? What resets it (e.g. power on/off, battery swap, memory lost, etc...)?


The so-called "contrast" setting is really a viewing-angle setting, otherwise we would just set it for max all the time. Sometimes it is appropriate to adjust it as battery voltage drops, in order to maintain the optimum viewing angle. It's more of an issue in low-duty-cycle LCDs though, mostly meaning graphics LCDs or large character-only LCDs. The 41's LCD hardly qualifies.

There never was a "fullnut" though. Before the "halfnut" was the "coconut"!


Hi, Egan;

the contrast settings remains after being set, i.e., depends on calculator main hardware. It uses a four-bit range parameter (0 to 15), usually in the X-register. If you have HEPAX, try HEPAX function 005. Default contrast is 5 (0101) instead of expected 7 (0111)... Go figure!

And, yeap: contrast setting remains after MEMORY LOST, but I do not know how long does it take to restore to default after being without batteries... i.e., IF it restores.



(After posting, I edited to add that HEPAX 005 actually uses X-register contents, and I left my HP41 without batteries after a MEMORY LOST for some more than 1 hour and the contrast restored to default, then.)

Edited: 6 Oct 2009, 8:59 p.m.


Interesting question. Do they show signs of fading?

I recall reading that Nikon originally designed all their top-of-the-line professional cameras with removable meters, because they expected the electronics to give out before the mechanicals. This has proven true. Nikon F2 cameras were built to last forever, and they do, but the meters don't.

Nikon also at first resisted using LCD's, because of concerns about the life span. Finally, someone decided that changing market conditions made this a moot point, since any new camera model would be obsolete long before it gave out. This has also proven true, since the 1980's F3's (the first with LCD's) are still going strong (for those who use them), but Nikon has since stopped making nearly all film cameras, and the digitals have only about, what, a 3-year model life span?

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