My backlight just went out one day on my laptop. After browsing around, I found that it was most likely the inverter chip. I found a replacement one and put it in. The backlight worked great for about 1 day. During that time, I had taken the opportunity to fix a noisy CPU fan and clean out the dust from the heatsink. By the time I had everything back together, the backlight wouldn't come on again. I assumed that the inverter had failed, and tried another one. Still no backlight. Either I messed something up when I had it open, or I have developed another problem.
I tried checking the voltage coming out of the High Voltage side of the inverter, and it stays at just around 5VAC on my meter. I thought that this meant that the inverter wasn't working properly, but I have since read that the inverter will probably switch off if the light isn't attached.
The input to the inverter is a 6 pin connector. I checked the continuity of each line on the cable, and even took off the fiber wrapping to verify the wires were not shorted, and everything looked fine. It appears that two lines are +5V, two are ground, and there are two other independant lines. One is at +2V and the other is at 0V. I know that there is probably a line to tell the inverter to turn on, and one to determine how bright to make the backlight. I am guessing that the 0V is the actuation line, but I am hesitant to pull it up to +5 without being sure. I traced that line to a riser board and down to the video card, but will have to dismantle most of the laptop to extract the video card and trace it further. I can do this if needed.
I should point out that the LCD appears to function correctly, at certain angles I can clearly make out the data on the screen, and it looks fine.
I am a novice at electronics repair. I am a software engineer but am making my way into electrical engineering. This will be my first repair of this sort.
My tools are somewhat limited, I have a nice multimeter, and an old scope.
In you guys' expert opinions, where should I go from here? I have a hard time believing that I was shipped two defective inverters. Could the first have blown the CCFL? How can I be certain without dismantling the LCD unit? How likely is it that something on the video card is going haywire when the LCD image is fine? I didn't disturb the video card when messing with the cpu fan.
I will be glad to give more details, pictures, run tests etc. Just let me know what you need.
Thanks,
Andrew