LCD Backlight Causing Motherboard noise

[amromlab]

The motherboard of my VGN-FS215M all of a sudden started making a high pitched noise whenever I run the laptop on battery power. The pitch differs according to the LCD brightness level. Even at full brightness the noise is very high. When the battery is drained to about 60 %, the LCD backlight flickers and turns off completely and the noise from the motherboard stops. Turning the backlight on again only brings the loud noise back and then the backlight flickers and turns off after a very short time. None of this happens while running off AC power. On AC power, I can work on the laptop for about forever without any noise or flickering. I suspected a backlight inverter problem, but all people who have inverter problems report noise from the inverter itself (not the motherboard) and it doesnt matter whether running on batteries or AC power. Could the inverter have 2 power supplies, one from AC and the other from the battery? Or is it a serious motherboard issue? Any suggestions?

[Blencogo]

Hi amromlab,

I don't have an answer but I would suspect that when using battery the inverter is not getting enough voltage. This could be caused by a few things: -

Dying Battery not giving enough power
Bad battery contacts
Faulty power regulator board (not sure if this is part of the mobo or a separate bit)
Faulty wiring.

I would try borrowing a battery if you can to see if this cures it - if not, it's off to the repairers.

Unless you want to have a look yourself - manual is attached! Looks like only one power cable to the inverter!

[amromlab]

Well, I bought a new high capacity battery. The noise is still there. The only improvement is that the backlight stays on longer while the motherboard is producing the same noise.