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LCD Woes




 
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W1RKW
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« on: January 09, 2005, 03:57:36 PM »

Anyone know if it is possible to fix an LCD that exhibits a poor viewing angle?  Looking at it dead on or at an upward angle is faint to non-existant but looking at it at a very downward angle looks good.  I've seen this on many things but have never figured out why LCD's do this. Any ideas?
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Bob
W1RKW
Home of GORT. A buddy of mine named the 813 rig GORT.
His fear was when I turned it on for the first time life on earth would come to a stand still.
K1KP
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LCD
« Reply #1 on: January 09, 2005, 08:51:34 PM »

Generally, the viewing angle on an LCD is something that is designed in and can't be tweaked once the thing is manufactured. However, most LCD displays have a contrast adjust pin. This might not be brought out to anything useful depending on your device (you didn't say what its in - Cell phone, calculator, etc) but if you can find the pin and adjust the voltage on it, you can adjust the contrast and this may help the viewing angle.
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KA1ZGC
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« Reply #2 on: January 11, 2005, 04:32:34 PM »

Quote from: K1KP
Generally, the viewing angle on an LCD is something that is designed in and can't be tweaked once the thing is manufactured. However, most LCD displays have a contrast adjust pin. This might not be brought out to anything useful depending on your device (you didn't say what its in - Cell phone, calculator, etc) but if you can find the pin and adjust the voltage on it, you can adjust the contrast and this may help the viewing angle.


I've had to do this a few times, and it's not so bad if you don't mind surface-mount soldering on some of the newer stuff.

The contrast of the LCD is determined by the potential on the aforementioned pin, sometimes it's pulled up from ground, sometimes pulled down from V+. Try googling any markings on the module and see if you can find a spec sheet on the thing. If it's in a Japanese radio, you'll probably strike out, but it's still worth a try.

Even if you can't, you usually only need to follow any branches off the power lead (or return lead), one of them will lead to the contrast pin.

LCDs work like voltage-controlled venetian blinds, the contrast is totally dependent on your angle with respect to the display. The voltage on the contrast-adjust pin is a biasing voltage to set the base angle. "On" is always 90 degrees from "off", no matter how it's biased.

Sooooo, if you can find the resistor in question, you can shunt some resistance momentarily to determine if it alters the contrast. If one does and the others don't, you found your fixed-value contrast bias resistor.

All you need to do at that point is pull the resistor and replace it with a suitable PC-mount pot. It'll be a little JS, but what project is complete without the ever-so-important JS clip lead?

On the other hand, you may find the resistor is just plain bad, and repacement with the intended value may put your viewing angle back in front of the display again.

Hope this helps... good luck!

--Thom
Killer Album One Zappa's Greatest Compositions
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Mike/W8BAC
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« Reply #3 on: January 11, 2005, 05:17:44 PM »

As mentioned above "LCDs work like voltage-controlled Venetian blinds". a detail not mentioned but equally important is the display is coated on the outside with a passive polarized plastic film or filter. The same type of polarized system used in sunglasses. When you buy a new item with an LCD display it usually has a protective plastic film over the polarized film to protect it.

If the polarized film is removed (hard to do) the display will vanish. If you use a harsh chemical to clean the film or put fine scratches on it by rubbing you can ruin it's optical clarity.

It sounds like the polarized film you have on that display may have been defective.

Mike
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K6IC
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« Reply #4 on: January 11, 2005, 06:01:04 PM »

Also,  I have noted that LCD Displays in my battery operated clocks and thermometers get a weaker and weaker display,  with ever narrowing vewing angle as the batteries go dedeer and deader.

SSSOOOOOO,   might also check the power supply voltage.

Good Luck    Vic   KF6RIP
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W1RKW
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« Reply #5 on: January 11, 2005, 06:10:58 PM »

What's happened over time with the handheld is the display has gradually degraded to viewing it at a very low and narrow angle. I suspect the bias voltage to the display is the culprit however, I haven't pulled the handheld apart yet.

I don't think it's a worn front panel lens as it's always been covered with something to protect the display.  It's just simply degraded over time.  I'll know better when I rip it apart.

Thanks for the tips everyone.
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Bob
W1RKW
Home of GORT. A buddy of mine named the 813 rig GORT.
His fear was when I turned it on for the first time life on earth would come to a stand still.
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