Digital LCD display defects ghosting

May 02, 2005 2 Replies
W

I have a handheld battery powered instrument with a LCD display that has a sort-of ghosting appearance (slow transition response?).



The readings are stable, they aren't drifting or searching for a reading, as they might if the input components were out-of-spec.



(1) The digits change slowly (2) the display looks different when viewed at an angle for certain readings.



When the decimal point is in one place, the digits look normal.. but when a different range is displayed, the display looks OK viewed straight on, but looks like it's all eights (88888) when viewed from an angle (off center from the left side).



Is it likely that the slow transition time is a fault/result of the A-D converter/driver IC? It's a socketed Intersil ICM 7211AIPL 40-pin device.



Would the ghosting be related to a backplane or a DP signal?



Do polarizer filters go bad? If one is utilized I suspect that it's bonded to the LCD.



I've inspected and cleaned the zebra strips and board pads for the display signals, and the same symptoms are still present.



Any suggestions would be appreciated



Thanks WB


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If you have multiplexing with numerous backplanes then it does not take much drift in the relative voltage steps to affect the output response as far as visibility. Suggest checking the supply to whatever sets these multiplexed steps

Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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W

Thanks Nigel, I'll see if I can locate the ADC/driver datasheet to follow your suggestion (maybe Jameco or other supplier will have one available).

Fortunately, I have a couple of these instruments (thermocouple calibrators), so I should be able to determine what the correct levels should be.

Cheers WB ................

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