Compaq V6500 Laptop Repaired By A Bright Idea
A customer bought in a Compaq Presario V6500 Laptop for repair. After switching on the computer, nothing could be seen on the screen. I shone my bright LED light onto the screen and could make out a faint picture of the windows start up screen.
From my research the problem appeared to be either the inverter or the backlight to be the most likely culprit.
According to some more research, a CCFL inverter is an electrical inverter that supplies alternating current power to a cold cathode fluorescent lamp (CCFL). CCFL’s are an older technology and for the moment are the most widely used backlights in laptops LCDs, but LED backlights are becoming more common. They consist of a fluorescent tube connected to a voltage inverter board which provides power to the backlight. Sometimes the backlight contains 2 tubes along with 2 pairs of inverters. The next generation’s inverter technology for the CCFL Lighting is the current resonance type inverter circuit. The resonance current which causes at the secondary side of the transformer is directly switching the primary side of the transformer through the switching transistor. It simplifies the circuit and improves efficiency.
THE DIAGNOSTIC PROCESS
The customer wasn’t in a rush to get the laptop back as it was mainly used by their daughter to play games. This gave me an opportunity to do some experiments and test different methods.
I was able to purchase a cheap generic inverter from Ebay http://www.ebay.com.au/itm/12-24V-CCFL-Inverter-Tester-LCD-TV-Laptop-Screen-6-32inch-Backlight-Lamp-Test-/400894850329?pt=LH_DefaultDomain_15&hash=item5d5731f519 for about $7 Australian with free postage.
I connected the Ebay inverter and still nothing appeared on the screen.
How could I be sure that the CCFL had blown and I didn’t have a faulty generic inverter? I didn’t want to buy another one to find that I had a different fault.
Please be aware! Inverters may put out up to 1.5Kv AC on start-up and 500 – 700 Volts during running, which I discovered the hard way. Now I also have a multimeter to repair as well…………Ah well, just another repair, another article to write! Please be careful when dealing with an inverter. I was able to also check the frequency input with my oscilloscope. So I knew the laptop was providing the correct voltage and frequency.
By putting my multimeter on the frequency range and keeping the leads close together, but not touching, even on the outside of the laptop, a frequency reading could be obtained and the inverter can be tested for operation. This method also worked. You may check out the link below for more information:
I searched the net for some direction. I found a bright idea – by cutting a compact energy saving house fluro light in two, I could separate the globe section from the inverter.
After cleaning up the wires, these could be connected to the inverter of the laptop, and hey presto! – it worked. This showed that the laptop inverter was fine and only the CCFL backlight had blown.
It was quite a task to remove the screen. Screws, tape, frames and more tape held it in place.
I carefully remove the tape as I believe it is used to stop bleed out of the lighting from the sides. As I pulled it down, I could see that the end of the fluro tube had broken off, possibly from the laptop being dropped.
After changing the new CCFL and reassembling all the tape, screws and frame, I was able to start up the laptop and the screen shone with the correct brightness. The customer also mentioned that they had some virus issues, so I attended to these. So when I asked for their password, they told me –password. Will people never learn?!
This article was prepared for you by Mark Rabone from Australia.
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