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HP Forum Archive 07

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Dim 15C display
Message #1 Posted by Stretch on 20 Nov 2001, 6:06 a.m.

Hi all,

I have a 15C which has not been used for a few years. I put fresh batteries into it and all seems ok until the LCD has to display more than 6 digits. The display then starts to lose segments. Reducing the digits displayed (say, fix2) and everything is ok again. No calculating errors occur so it is only a display glitch BUT when doing a selftest (on & x) however, all the LCD sements working perfectly. Any ideas??


Re: Dim 15C display
Message #2 Posted by David Smith on 20 Nov 2001, 5:41 p.m.,
in response to message #1 by Stretch

You might try letting it run for a few days (try a program that displays -8888888888-88, pauses, and loops forever so the machine does not time out). I have seen some LCD displays that seem to need some exercise before they work properly... but not on a 15C type of machine though.

Re: Dim 15C display
Message #3 Posted by Vieira, Luiz C. (Brazil) on 20 Nov 2001, 8:40 p.m.,
in response to message #2 by David Smith


I think this is interesting. I read some stuff about LCD some time ago, and the fact they can stress with time and become less readable (say, no such contrast as before) made me think seriously about their performance. That`s the first actual case I`ve been told about.

Please, Dave, you mentioned you have seen some LCD`s that needed some exercise. I`m curious about it. Would it be due to some specific working condition? I mean scan frequency, reference voltages, environment preassure, temperature and light condition, type of light when ON or OFF, and the like. Do you have more information about it? I`m not specifically concerned about my HewPack calcs, but also about LCD`s used in industry, field eqpt, measurement instruments, etc. I used to think that, as many semiconductors, LCD`s would rest as long as they were working. Of course, reading about them and knowing their crystal structure is far from the SI or GE semimetals cleared my mind (college golden times).

I'd be glad for any info you can share.


Re: Dim 15C display
Message #4 Posted by David Smith on 21 Nov 2001, 4:58 p.m.,
in response to message #3 by Vieira, Luiz C. (Brazil)

I'm not sure of the exact cause. I have personally seen it happen in some old LCD panel meters. Possible causes are the LCD material becomming "sticky" or its makeup becomming separated without use, buildup of residue in the material or on the indium tin oxide electrodes, etc. I think they just need some regular exercise... just like electrolytic capacitors.

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