LCD display question

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dacflyer
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LCD display question

Post by dacflyer »

i have a bunch of LCD displays, all save same problem... very dim display... but the contrast control works just fine, from nothing to all black..
do LCD's wear out ? if they do , then the contrast should have no effect?
curious if something else may be wrong with the displays.. they are quite expensive to replace..
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Janitor Tzap
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Re: LCD display question

Post by Janitor Tzap »

Have you checked the CFL tubes?

Like regular fluorescent light bulbs, as they age they will dim, till finally they burn out.


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dacflyer
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Re: LCD display question

Post by dacflyer »

this is not that type... this is just plain LCD, like watches have...black digits on grey background, but way bigger..
240 X 128 "DMF5005N"
they have lousy EL backlights as well..but backlight is not the issue..

link of what it looks like..
http://yahoo.aleado.com/lot?auctionID=e191061252
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Janitor Tzap
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Re: LCD display question

Post by Janitor Tzap »

Okay I see what your talking about now. :lol:

Hmmm.............

Have you tried putting a bit of pressure on the display with a finger?
Do the characters lighten or get darker?

I'm thinking that the liquid chemical in the substrate is breaking down.
Thus, the characters are lightening up.

Strange....
I normally see the chemical liquid has seeped out from between the Glass substrates and Polarizing filters.
This makes the characters only partially visible.

From Wikipedia: https://en.wikipedia.org/wiki/Liquid-crystal_display


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CeaSaR
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Re: LCD display question

Post by CeaSaR »

Does the display need an external power supply or is it driven by the data connections? (Just checking the obvious)

How is the display connected to the board, soldered, wires, or foam contacts? If it is foam contacts, they could be dirty or even losing their springiness,, thereby not putting enough pressure on the contact(s).

Or, as JT pointed out, the liquid may be leaking.

CeaSaR
Hey, what do I know?
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dacflyer
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Re: LCD display question

Post by dacflyer »

the displays are attached to another control board.. cable connections.
these displays are well over 10-12 yrs old. used on traffic signal controllers.
we been just replacing the whole front panels. but i am just curious if the LCD's are worn out or if there might be something common failing.
the cabinets are in the sun, and have cooling fan in them, but the insides can still get very hot.. over 120F some days.
i am thinking also that the LCD's might be just cooked or frozen to death over all the years.
wish there was a drop in OLED Display.. would make for way easier reading in the sunlight. or at night.
the internal EL backlight for the displays suck big time.. and the cabinet light is of no use.
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Re: LCD display question

Post by haklesup »

It is likely that the liquid crystal between the glass gradually leaked out or degraded over time due to thermal stresses
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Re: LCD display question

Post by Janitor Tzap »

Hmmm..........

I wonder if you couldn't replace the LCD with a VFD {Vacuum Fluorescent Display}?
Image
It would be more rugged then the LCD, and better suited for outdoor devices in cold climates.
Only draw back is they have a higher voltage requirement, and use significantly more power (0.2 watts).


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Re: LCD display question

Post by haklesup »

only if the data bus and control lines are compatible in terms of codes transmitted as well as logic voltage levels. Supply voltage differences are easier to overcome. A study of both datasheets is required to answer that. For example replacing a parallel bus display with a serial one would be fruitless. However, it is very possible that there is a compatible enough one somewhere
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Re: LCD display question

Post by dacflyer »

VFD would not work, as it is not a drop in replacement..
i have seen OLED versions, but not sure if they are compatible units, and or fit the same..
i do not know why they do not make them yet at this day and time of technology..
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Re: LCD display question

Post by Janitor Tzap »

From Wikipedia:
Disadvantages

Lifespan
The biggest technical problem for OLEDs was the limited lifetime of the organic materials. One 2008 technical report on an OLED TV panel found that "After 1,000 hours the blue luminance degraded by 12%, the red by 7% and the green by 8%."[68] In particular, blue OLEDs historically have had a lifetime of around 14,000 hours to half original brightness (five years at 8 hours a day) when used for flat-panel displays. This is lower than the typical lifetime of LCD, LED or PDP technology. Each currently is rated for about 25,000–40,000 hours to half brightness, depending on manufacturer and model.[69][70] Degradation occurs because of the accumulation of nonradiative recombination centers and luminescence quenchers in the emissive zone. It is said that the chemical breakdown in the semiconductors occurs in four steps: 1) recombination of charge carriers through the absorption of UV light, 2) homolytic dissociation, 3) subsequent radical addition reactions that form π radicals, and 4) disproportionation between two radicals resulting in hydrogen-atom transfer reactions.[71] However, some manufacturers' displays aim to increase the lifespan of OLED displays, pushing their expected life past that of LCD displays by improving light outcoupling, thus achieving the same brightness at a lower drive current.[72][73] In 2007, experimental OLEDs were created which can sustain 400 cd/m2 of luminance for over 198,000 hours for green OLEDs and 62,000 hours for blue OLEDs.[74]

Color balance
Additionally, as the OLED material used to produce blue light degrades significantly more rapidly than the materials that produce other colors, blue light output will decrease relative to the other colors of light. This variation in the differential color output will change the color balance of the display and is much more noticeable than a decrease in overall luminance.[75] This can be avoided partially by adjusting color balance, but this may require advanced control circuits and interaction with the user, which is unacceptable for users. More commonly, though, manufacturers optimize the size of the R, G and B subpixels to reduce the current density through the subpixel in order to equalize lifetime at full luminance. For example, a blue subpixel may be 100% larger than the green subpixel. The red subpixel may be 10% smaller than the green.

Efficiency of blue OLEDs
Improvements to the efficiency and lifetime of blue OLEDs is vital to the success of OLEDs as replacements for LCD technology. Considerable research has been invested in developing blue OLEDs with high external quantum efficiency as well as a deeper blue color.[76][77][78] External quantum efficiency values of 20% and 19% have been reported for red (625 nm) and green (530 nm) diodes, respectively.[79][80] However, blue diodes (430 nm) have only been able to achieve maximum external quantum efficiencies in the range of 4% to 6%.[81]

Water damage
Water can instantly damage the organic materials of the displays. Therefore, improved sealing processes are important for practical manufacturing. Water damage especially may limit the longevity of more flexible displays.[82]

Outdoor performance
As an emissive display technology, OLEDs rely completely upon converting electricity to light, unlike most LCDs which are to some extent reflective. e-paper leads the way in efficiency with ~ 33% ambient light reflectivity, enabling the display to be used without any internal light source. The metallic cathode in an OLED acts as a mirror, with reflectance approaching 80%, leading to poor readability in bright ambient light such as outdoors. However, with the proper application of a circular polarizer and antireflective coatings, the diffuse reflectance can be reduced to less than 0.1%. With 10,000 fc incident illumination (typical test condition for simulating outdoor illumination), that yields an approximate photopic contrast of 5:1. Recent advances in OLED technologies, however, enable OLEDs to become actually better than LCDs in bright sunlight. The Super AMOLED display in the Galaxy S5, for example, was found to outperform all LCD displays on the market in terms of brightness and reflectance.[83]

Power consumption
While an OLED will consume around 40% of the power of an LCD displaying an image that is primarily black, for the majority of images it will consume 60–80% of the power of an LCD. However, an OLED can use more than three times as much power to display an image with a white background, such as a document or web site.[84] This can lead to reduced battery life in mobile devices, when white backgrounds are used.

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dacflyer
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Re: LCD display question

Post by dacflyer »

how much of this is true for monochrome displays ?
would be neat if the manufacturers designed the display to go blank after a time out.
maybe i ought to call and talk to them, see what they think..
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Re: LCD display question

Post by haklesup »

Many displays have a way to turn off the display, sometimes the contrast voltage can do the same or perhaps the chip enable pin would be most universal, one can also pull the plug on the display by putting a soft switch in series with the VDD pin. The blanking would be controlled by the app circuit not necessarily the display.

I don't think they make monochrome OLED but if they did, I wouldn't expect lower supply current, that's going to be based on the technology of the display. Certainly there are things that auto power off like a digital fever thermometer. Color LCD are more complicated and probably do consume more power as they have to scan 3 arrays of pixels instead of one and are usually capable of moving graphics. That tends to be a dynamic refresh while monochrome can use static almost combinational logic for control. VFD tends to be monochrome all the time.

I wouldn't assume the info on Wiki about power consumption will remain accurate for all time. Product development on all types of displays could change the required current perspective. I suspect the comparison of OLED to LCD is for dynamic graphics displays not the low power static character only displays. I'm not sure they even make character only OLED.
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Re: LCD display question

Post by dacflyer »

i'd not be too concerned about power consumption...
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