Capt. Paul:
I inadvertently left my hand-held GPS unit in my car on the dashboard near the windshield. It was there about five hours in the middle of the day and in the sun. When I picked up the unit, it was hot to the touch. When I turned it on, there were heavy black parallel horizontal lines across different sections of the screen. These lines stayed there regardless what different screen I selected. What happened, and can I correct it?
Ralph P.
Tampa, Fla.
Ralph:
You did not say what brand or model of GPS you had, but it probably is a unit that uses a liquid crystal display (LCD) to configure and produce the images on the viewing screens. LCD units are most susceptible to outside heat.LCD units have very small crystals made into the screen to produce the total overall image. Depending on the temperature and particular nature of a substance, liquid crystals can be in one of several distinct phases.
One feature of liquid crystals is that electric current affects them. A particular sort of liquid crystal, called twisted nematics, (TN), is naturally twisted. Applying an electric current to these liquid crystals will untwist them to varying degrees, depending on the current’s voltage. LCDs use these liquid crystals because they react predictably to electric current in such a way as to control light passage.
A very small electrical current is directed to each individual crystal. It is used to produce a shade different from the background. The electrical current produces a very small amount of heat, and causes the individual LCD to change its reflective ability, and appears darker. A group or series of these crystals with different shades make up the lettering and images that you see on the screen.
Unfortunately, heat from other sources can also affect the crystals. The liquid crystals are very sensitive to temperature, and are why they are used to make thermometers and mood rings. It also explains why a laptop computer’s display may act funny in cold weather or during a hot day at the beach.
You may have noted what the owner manual listed as an operating range for the unit. It is probably somewhere between 0º and 160º. Evidently the heat accumulated in your unit was above that range while it was on your dashboard in the sun. The heat buildup caused the LCDs to react to the heat, causing them to turn dark. The LCD crystals may have been damaged. Unfortunately, the lines may be permanent.
I had it happen to me one day when fishing in the heat of July. I was fishing at a particular location for over two hours. When I looked at the unit, there were black lines across the face of the display; some were internment. I immediately turned the unit off, dampened a cloth in ice water and placed it over the unit for an hour and, with my fingers crossed, turned the unit back on. Fortunately, I caught the problem before it became permanent. When the unit “rebooted,” the screen was normal. I was lucky.
You may try leaving the unit off and place it in a cool environment for a few days. Then reboot and see if the lines are still there. If they are, the only remedy is a trip to the manufacture’s repair facility.
This outside heat problem is why most “marine” GPS units are manufactured with a silver, white or light-colored case. The lighter colors do not absorb the sun’s heat as would a dark color.
Simple remedy: Shade them from the sun.
My fishing GPS unit is a handheld that I mount on the center console of my bay boat. To defeat the heat problem during a day on the water, I now use a small white cloth to cover the GPS and the depth finder units. My wife sewed an elastic band and Velcro strips on one edge of the cloths. I then attach the cloth to the top of my units. When under way there is usually no need to have the units covered. But, when not moving, I simply flip the cloth over the top and face of the unit. I have yet to have a display become distorted using my cloth “shield.”
Newer units use an improved type of display. Some of the new-model GPS, depth-finders, radios and cell phones use a Film Compensated Super Twisted Nematic (FSTN) crystal. It too, however, is sensitive to excessive heat and cold, but appears to be an improvement over the LCDs.
This type of crystal provides a better contrast, but is also more costly. The major benefit is the improved contrast ratio, and it is not quite as sensitive to outside heat sources. The contrast ratio is better than the LCD, in that it offers a much-lighter color background and darker pixels.
If you have to contact the manufacturer, try their support section on the Internet or check your user’s manual for a telephone number.
Got a GPS question for Capt. Paul. Ask it on louisianasportsman.com, and he’ll answer it, either here or on the Web.
