HP Forum Archive 10

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Working Lifetime of LCD Displays Message #1 Posted by Nick Nicholas on 30 Jan 2003, 4:22 a.m. I read somewhere that the LCD displays have a limited lifetime and that is why LCD calculators have limited value as working collectables. Other than the batteries of the older calculators, are there other components of the calculator that may have a limited time before they degrade and are no longer functional?

Re: Working Lifetime of LCD Displays Message #2 Posted by John Smith on 30 Jan 2003, 6:47 a.m., in response to message #1 by Nick Nicholas If there's actually some limit to the useful life of LCD displays it must be quite high, indeed. I have a number of very early LCD calculators in my collection, some of them of the 'first-batches' yellow LCD type, and not only do they still work fine, but I can't notice any sign of degradation or diminished functionality whatsoever, despite the fact of them being 25+ years old.

Re: Working Lifetime of LCD Displays Message #3 Posted by Grant Goodes on 30 Jan 2003, 10:11 a.m., in response to message #2 by John Smith The lifetime of first-generation LCD displays is highly variable, and probably dependent on the temperature extremes to which they are exposed. My only LCD calculator is my 41CX, but I have additional experience with Nikon F3HP ("High eyePoint", not Hewlett Packard!) cameras which use a miniature LCD display in the viewfinder. These cameras came out in 1979/80, much like the HP-41C. The displays of Nikon F3 _do_ loose contrast over time, eventually becoming virtually unreadable, but not every F3 seems to suffer from this. No one really knows, but speculation among F3 users is that the extremes of temperature that these cameras can be exposed to by their (often professional photog) users accelerates the problem. My 41CX almost never sees anything but room-temperature, while my Nikon F3/T gets everything from arctic to desert. grant..

Re: Working Lifetime of LCD Displays Message #4 Posted by Tom (UK) on 30 Jan 2003, 12:45 p.m., in response to message #1 by Nick Nicholas I think LCD's are more prone to physical damage, e.g. temperature, shock, delamination etc. So if you look after them well they should last a long time. LED displays seem more prone to electrical faults in the driving circuitry, I'd guess this is due to the much higher current being drawn. I don't know what the fail mechanism is for LED drivers, I'd guess burnout of the driving circuit or electromigration (over a very long time the internal wiring of the ic gets thin and eventually 'snaps' due to the high current density). If you own an HP calc it doesn't matter what the fail mechanism is, it still stops working (both are repairable - replace the LED driver or replace the screen). From this forum there seems (to me) to be more postings about LED problems than LCD - this would imply that 'well looked after' LCD calcs are more reliable than LED calcs but may also be due to LED calcs being older, or users just acepting that LCD's fail so are not too bothered about asking for help. my 2 pennies worth

Re: Working Lifetime of LCD Displays Message #5 Posted by David Smith on 30 Jan 2003, 5:55 p.m., in response to message #1 by Nick Nicholas Some early LCD's had problems with contaminates in the goo that over time caused it to decompose. This does not seem to be a problem with HP LCD's. Early LEDs had problems in the bonding and processing of the gallium arsenide/phosphide/etc semiconductors. I have seen quite a few bad LED displays in HP calculators. The only LCD faults were caused by physical damage or dirty interconnects.

Re: Working Lifetime of LCD Displays Message #6 Posted by Gordon Dyer on 30 Jan 2003, 6:54 p.m., in response to message #1 by Nick Nicholas I did some reliability testing of LCD displays in the early 80s. They will last for a very long time if they are stored and used at room temperature and with the humidity level not too high. High humidity can be a killer for early displays and so can any contaminants introduced in the manufacturing process. So dont store them outdoors in damp conditions.

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