Laptop LCD Screen Displays Is Dim or Dark
Published: 08th April 2015
A laptop with this type of problem will still display images normally but the image will be very faint or dim because there is no backlight to illuminate or brighten the image. The two common faults that can possibly cause this type of problem are burnt out or dead CCFL tube/backlight or a faulty LCD inverter. To troubleshoot effectively, you need to open up the laptop screen, before doing this refer to instructions specific to the laptop in question. During disassembly of the screen, take note of the points where each screw is before it was removed, so that you wont have any problem or difficulty in assembling the screen back.
Built out CCFL tube or backlight
Faulty LCD inverter
The laptop motherboard does not supply the LCD inverter with the 5V needed to power the CCFL tube/backlight
The laptop LCD lid close switch is stuck in the close position
After opening the LCD screen panel, bring out the CCFL tube and check for clear signs of burning of the tube, if signs of burns is visible on the tube then it means that it is burnt and needs to be replaced but if not, just power the laptop with all the component plugged in but disassembled. If the CCFL tube lights up, then there is nothing wrong with the tube.
Once the CCFL tube/backlight has been confirmed to be working, the next step is to confirm if the LCD inverter is getting the 5V required to power the CCFL tube/backlight from the motherboard. This is very important because the function of the LCD inverter is to transfer power to the CCFL tube/backlight from the motherboard.
To confirm if the LCD inverter is getting the required voltage from the motherboard, turn on the laptop (remember it is still disassembled) take your multimeter, switch it to D.C voltage and let it be within the range of 5V, use the meter to read the voltage of a component (e.g. an electrolytic capacitor) on the LCD inverter circuit.
If you get a voltage value of 5V or something close to it then it means that the LCD inverter is being supplied with the required voltage, which implies that the 5V supply from the motherboard is not the problem. But if it turns out that there is no supply of 5V from the motherboard to the LCD inverter, then it means that you have to jump or transfer 5V from the motherboard to the inverter.
To do this, look for a light wire, locate a component with 5V DC supply on the motherboard, then use the wire to tap or jump the voltage from the motherboard to the inverter (the positive terminal of any component e.g. an electrolytic capacitor on the LCD inverter circuitry will serve the purpose) with this done, provided the LCD inverter itself is ok, the CCFL tube or backlight should start functioning again and image on the laptop screen becomes bright and visible again.
In some rare situation, after all the above possible cause of fault have been ruled out or confirmed. The LCD lid close switch might just be the cause of the problem, this is possible if it is stuck in the close position. In this mode the CCFL tube/backlight stays off. This is to save or conserve power, when the laptop is ON with the lid closed. To release the lid which is often times located near the hinges of the laptop screen from the close position, just press it so that it can come up or use something to raise it up. You can also check the brightness and contrast setting of the laptop just to be sure.
Charles Obodo is an experienced laptop engineer whose basic goal and aim is top give relevant information to help solve and fix all laptop problems. His personal blog is http://learnlaptoprepair.blogspot.com and you will find quite a lot of helpful resources on the site.
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