Adjusting LCD contrast potentiometer???

[Reo51St]

Does anyone know the proper way to adjust the contrast potentiometer on the back of an LCD???

Is it purely a sight adjustment or is there a place it should be measured???

Or should it just be left alone???

Thanks for any help.

[gator]

Are you talking about laptops or desktops? I don't remember seeing a pot anywhere on any of the systems I have used - unless you are mentioning any pot that is there in the back of the LCD panel itself (I mean inside the casing). Can you make your question bit more clear?

[Reo51St]

It seems that most L.G. Philips LCD’s have a potentiometer on the circuit board on the back of the LCD.

11P8241
11P8295
11P8293
46L4295

When adjusting contrast will go from one extreme to the other.

Would like to know if it is just up to my opinion of what looks good to me or is there a way to measure??? Or is there a test screen that is used to do this adjustment to.

Thanks for the help.

[SMA]

gator - the 600x you have in your signature has a brightness pot.

[gator]

SMA, I know - but the one on the 600X is for brighness, and the OP's question was for contrast. Even the famed IPS screens dont have hardware contrast adjustment ...

[rkawakami]

Would like to know if it is just up to my opinion of what looks good to me or is there a way to measure??? Or is there a test screen that is used to do this adjustment to.

My thought would be that you need some sort of a gray scale bar display such as the one here:

http://lcdresource.com/mambo/index.php? ... &Itemid=36

[TTY]

Or is there a test screen that is used to do this adjustment to.

Here is another utility for adjusting contrast, and in my post in this thread, you'll find a description on how to use it.

[Reo51St]

Sorry for any confusion I may have started but while testing some LG’s “Over 300 to test” I found a pot on the back of the LCD’s.

I was hoping that it was for brightness as most of the panels are dim and some had poor picture quality. As I adjusted it the brightness did not seem to increase or decrease but picture quality did so I assumed it was contrast. ”Maybe focus???”

Ray thanks for the link it will give me something to try in the morning when I get to work. Gray scale have not heard that for 25-30 years.

Any info I can get to save as many of these panels is very much appreciated.

Thanks for all responses.

[SMA]

So now the professionals in the industry are also seeking help at thinkpads.com

Well, I do not mind.

If the failure rate for the panels tested is too high, then it could indicate a problem with the test procedure.
It might be necessary to start by testing the test system and possibly retesting it at regular intervals.

If all the panels are being tested in the same ThinkPad system, then that could be the reason.

In my understanding, brightness is a matter of backlight. Which again is,
the panels capability to let the backlight pass through,
the CCFL located in the panel,
the inverter and
the cabling.
If the same lcd cable is used for testing 300 panels, then I would doubt that the connector
will still be able to make good contact when panel number 300 is being tested.

Technically, the motherboard is generating a low frequency square wave.
This signal is sent to the inverter where it is being used to modulate the high voltage ac signal generated by the inverter.
The modulated high voltage ac signal then goes to the CCFL, where its energy is converted to light.
The ratio between the on and the off periods in the square wave determines the panels brightness.

I do have some pictures of these signals. If so desired I can post them.
A little help or a link on how to add pictures would be helpful then.

And by the way, some of the legacy ThinkPad's did have user adjustable contrast pots, but those that did, did not have TFT panels.