I have a clock with an LCD, which has been in use for nearly 40 years (!), but the display contrast is now much less than when the clock was new. Is this inevitable with LCDs as they age, or would tinkering with the display bias voltage be likely to improve the contrast?

 

Usually there's a preset for contrast on lcd modules, but it may be set by fixed resistors. They are driven by out of phase signals compared to the backpane pin.

 

I believe that if the contrast improves when the display is seen from other angle; tells it can be tweaked. Where and how, I do not know and is probably different for every type of display.
I wish I knew...

 

They are driven by out of phase signals compared to the backplane pin.

Indeed. And it's my understanding that asymmetry of those anti-phase signals can cause deterioration. Since the display has lasted ~40 years I suspect the symmetry is pretty good. Perhaps there's some other aging mechanism?

 

I have a clock with an LCD, which has been in use for nearly 40 years (!), but the display contrast is now much less than when the clock was new. Is this inevitable with LCDs as they age, or would tinkering with the display bias voltage be likely to improve the contrast?

Not likely. The atomic structure of an LCD display is such that the molecules that make it up are in parallel or not in parallel, based on the supply voltage. When in parallel the supply voltage places these molecules into alignment When not in parallel you cannot see the display. Because the molecular alignment is set by the voltage. Furthermore, the reason a LCD display works with such high efficiency is that it takes almost no current to drive an LCD display. Being that you have an LCD display that is 40 years old, the molecular structure of the alignment molecules has been degraded. Sorry to have to give you the bad news, but for this reason I don't think there is much you can do to fix the problem.

 

Could be the polarizer is creating issues

 

Is the problem LCD contrast, or is dim LED backlighting? LEDs don't really fail for the mostpart, they just get dimmer and dimmer. LED lifetime is considered 50,000 hours, at which point the brightness will have decreased 50% from original. And after another 50,000 hours, it will fall another 50% from what it was (i.e., 25% of original).

 

Good point about the backlight. It's certainly dimmer than it was originally. But the backlight isn't on unless a momentary button is pressed.

 

Could be the polarizer is creating issues

Thanks to:
R!f@@

Kindness is the one thing we all need to practice more often (excellent advice)

 

Thanks guys. I thought the chances of being able to restore the contrast on this particular clock were pretty slim, but wondered if anyone had tried reviving an ancient LCD. I did have a couple of new old-stock LCDs (unknown brand) a few years ago and found that varying their bias voltage did indeed vary the contrast.

 

Thanks guys. I thought the chances of being able to restore the contrast on this particular clock were pretty slim, but wondered if anyone had tried reviving an ancient LCD. I did have a couple of new old-stock LCDs (unknown brand) a few years ago and found that varying their bias voltage did indeed vary the contrast.

I was playing with a nominally 3 Volt multiplexed display a couple of weeks ago and found that adjusting the bias down by just 0.1 Volts made a massive difference. So you may have to alter the whole supply voltage slightly, but it could be worth trying!