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Electronic help required - independently powering a CCFL Answered

Hi, a friend of mine recently had a problem with a laptop where the screen went dim. I tried the obvious, screen settings (it didn't have a monitor swith-off button :S ) and reset the bios with no luck, so I thought that the problem was probably related to either the cable, the inverter or the backlight. I tried a new lcd screen with a known-working backlight and it failed to work. I also purchased a new cable and a new inverter but the backlight still failed to turn on. This now points me in the direction of a motherboard problem. I am going to take a multimeter and test the voltages going from the inverter and to the inverter. If these appear to be correct, is there any way that I can get the backlight to turn on? If the voltages are correct I would assume it's something to do with the light control and stuff, and wonder if I was to say, disconnect all the wires from the inverter but dc supply and ground (and I think there is a connection to the oscillator?), would it work? If there is no voltage going to the inverter, does anyone know how I could power the backlight independently? I would imagine it would take some sort of power regulator and maybe a separate inverter? Thanks

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photozz (author)2007-02-04

well, the inverter will most likely take a straight 5v DC power. I have pulled inverters and tubes out of laptops before and powered them up. The challenge would be, I think, figuring out the pinout of the inverter. You should be able to apply a straight 5v to the power input and it should fire up.

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MoonDemon (author)photozz2007-02-04

I am wondering that if it's only 5V could it be powered from a usb port?

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eight (author)MoonDemon2007-03-23

One USB socket only supplies up to 500mA per plug @ 5 V DC This I think will be the problem. Drawing enough current without resorting to a powered USB hub. I buy many CCFL / Inverter combos to play with at home. These are all 12v. One x CCFL tube (12" - 300mm long) will draw about 350 mA at 12 Volts. Four x CCFL tubes (12" - 300mm long) will draw about 1400 mA at 12 Volts. You would need 3 independent USB ports. However, 12v switchmode power supplies have become cheap and tiny in size. I hope this has helped. By the way, I have attached the data from the wholesaler. Good Luck Mate !

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trebuchet03 (author)eight2007-03-23

One USB socket only supplies up to 500mA per plug @ 5 V DC

I think the device has to negotiate for up to a 500mA max. I believe the bus is 100mA max, unless the device asks for more......

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photozz (author)MoonDemon2007-02-04

possibly. It depends on the current draw. I would try to get it working off an external supply first. then once you have the wiring worked out, you can try the USB port.

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MoonDemon (author)2007-02-05

My problem actually may be related to a capacitor problem, as the board is reknowned for its crippled capacitors. I was wondering how I would go about testing them? Usually you can just stick a multimeter on it and it will read the capacitance, but generally speaking you need to remove the components from the board before you can do that. A power-related problem struck me because the latop used to hold 20 minutes or so worth of charge, but now it won't hold any charge (occuring at the time of the backlight power failure)

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