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Replacing CCFL backlight on a workstation

Discussion in 'Troubleshooting and Repair' started by splinters, Aug 19, 2011.

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  1. splinters


    Aug 19, 2011
    Bit of a strange one. I recently bought an Alesis Fusion workstation, the musical keyboard variety and it has a largish 4inch backlit LED screen. It appears to have been damaged in transit as the screen light would go on and off when the keyboard was rocked lightly. I suspected a loose contact and opened it up, reseated everything and it improved for a while but failed again. It looks like the small CCFL light has gone and the wires have now become detached so i have no idea if the bulb has failed or the inverter board.
    The tube is approx 2mm diameter (dont have a micrometer with me) and 80mm long.
    There is one for sale on ebay but it is 2.5mm diameter.
    My main question is, would this be a suitable replacement? There are rubber end plugs which should still fit over the extra .5mm and the seller says it should work.
    Problem is, i have no way of identifiying the bulb as the board is out of production and Alesis will not send a service manual. Are all bulbs the same voltage, power etc. Are they just based on length and diameter?
    Also, is there any way of checking the inverter board itself to see if it is the culprit i.e. Can i attach a cheap LED light or similar to the wires that were attached to the CCfL to see if it supplying power?
    Sorry for the long post, really need to get this sorted and, while i am able to solder the wires to the new light, i am no electronics expert.
  2. splinters


    Aug 19, 2011
    Just one more thing to ask, is there a particular way to wire up the tube? Both wires are plain white so i am unable to identify one from the other. Also, i noticed the backlight would not illuminate when the keyboard case (which is metal) was opened the first time i checked but it was fine once the case was closed. Should i be able to see the new CCFL illuminate before closing the keyboard back up or is there some sort of earth or similar that stops it from illuminating when the case is open?
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    I have changed a CCFL on 2 items of equipment. It's a job that needs to be done in as close t clean-room conditions as you can manage because in many cases you need to take the LCD display apart, and any dust that gets in will bother you for ever afterwards.

    The CCFL is also very brittle, and will apparently break if you look at them the wrong way. None of mine broke on removal or replacement, so they're probably a little more rugged than their reputation suggests.

    Although I've heard of some LCD displays that make the task of replacement relatively easy, every one I've seen requires you to take things apart that were never meant to come apart. Putting them back together (in my experience) left signs that things were not quite original condition.

    If you can get away without replacing the CCFL you'll be better off.

    From some brief research, it appears CCFL operate on AC, so it should not matter which way around the wires are connected. However, since one end is typically grounded, there may be one end of the tube that has better insulation or isolation than the other.

    The CCFL operate from a very high voltage, so there's not a lot you can do to test that voltage (other than another ccfl lamp).

    In my case, I knew the CCFL was at fault, and the combined cost of a CCFL and an inverter was low enough that I ordered (and replaced) both.
  4. splinters


    Aug 19, 2011
    Thanks Steve.
    I have the LCD out and the CCFL here in my hands so no worries on dismantling etc. The tube is pretty robust and is easily replaced back into the board. The wires have no identifying marks at all, nor does the CCFL so i cannot see how i would indentify one end from another. I can get the tube in a few days as it is in the uk but the invertor boards have to be shipped from the us and will cost £50+ whih i would like to avoid if poss. Would also take at least a week or two to get here. I wonder i my local maplins electronics store have any pc mods that would have a part in i could salvage just to test?
    The CCFL does have the rubber ends to cover the contacts.
  5. Resqueline


    Jul 31, 2009
    If the wires has come off the tube you can just try to resolder them to test.
    One of the wires is usually longer, running along the tube.
    The tubes are completely identical each end.
  6. splinters


    Aug 19, 2011
    Both wires have come off. However, there is hardly no electrode remaining to solder to. One wire runs to each end.
  7. splinters


    Aug 19, 2011
    Plan b seems to have failed. My local maplins had a 10cm blue cathode kit with an inverter ready wired up. I connected it to the board and it did not illuminate. The keyboard has two custom boards interconnected. One must be the inverter, no idea what the other one does but they are interconnected with a small 2 pin connector. I read that they both need replacing.
    I took both boards out and one of the resistors has burn marks around it so i guess i need two new boards as well as a CCFL.
    I tried connecting the power connector that connected to the first board into the inverter but the new ccfl did not illuminate so iam puzzled. I guess that is not a 12v supply?
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