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    Faking CCFL inverter

    Hey guys I was reading an earlyer thread on substituting a risitor for a ccfl lamp in a computer display.

    Here was Plain Bill's example:" Ohms law. At a rough guess a CCFL runs at 650 - 1000 Volts and draws 3-5 mA.

    E / I = R or 800/.004 = 200Kohms

    I X E = P or .004 X 800 = 3.2 watts

    So a 200K ohm, 5 watt resistor hooked to an appropriate connector should do it."

    Ok so my measurements were somewhat different. One lamp leg was 260 Volts and the current draw was 7.5 mA.

    E / I = R or 260/.0075 = 35Kohms it was acctually 34666.66667 so I rounded up.

    I X E = P or .0075 X 260 = 1.95 or 2 watts

    I have four ccfl lamps two on top two on bottom. I figured 260 fluctuating voltage time two lamps 520 volts for just that half of the inverter.

    I originally tried 160K 2 watt resistors two in series and although they kept the ccfls on, the resitors got extreamly hot so I abandoned that set up. So then I placed them in paralell cutting my resistance in half but still extream heat on the resistors and so no go. I wish I could measure the heat. Does paralell with resistors double there watt ratting or in series? or does the watt ratting stay the same no matter the configuration.

    So if my calculations are correct I would need 35K at 2 watts. Less resistance less heat. I think. So any ideas. I don't want to start a fire.

    #2
    Re: Faking CCFL inverter

    Originally posted by TrippKJ4BKD View Post
    Hey guys I was reading an earlyer thread on substituting a risitor for a ccfl lamp in a computer display.

    Here was Plain Bill's example:" Ohms law. At a rough guess a CCFL runs at 650 - 1000 Volts and draws 3-5 mA.

    E / I = R or 800/.004 = 200Kohms

    I X E = P or .004 X 800 = 3.2 watts

    So a 200K ohm, 5 watt resistor hooked to an appropriate connector should do it."

    Ok so my measurements were somewhat different. One lamp leg was 260 Volts and the current draw was 7.5 mA.

    E / I = R or 260/.0075 = 35Kohms it was acctually 34666.66667 so I rounded up.

    I X E = P or .0075 X 260 = 1.95 or 2 watts

    I have four ccfl lamps two on top two on bottom. I figured 260 fluctuating voltage time two lamps 520 volts for just that half of the inverter.

    I originally tried 160K 2 watt resistors two in series and although they kept the ccfls on, the resitors got extreamly hot so I abandoned that set up. So then I placed them in paralell cutting my resistance in half but still extream heat on the resistors and so no go. I wish I could measure the heat. Does paralell with resistors double there watt ratting or in series? or does the watt ratting stay the same no matter the configuration.

    So if my calculations are correct I would need 35K at 2 watts. Less resistance less heat. I think. So any ideas. I don't want to start a fire.
    I doubt you got an accurate reading on the voltage; that signal is an irregular waveform at 50 Khz or higher. Most DMMs can't handle it. Some fail spectacularly.

    A pair of resistors in parallel or in series have double the power dissipation capability of one (assuming you don't ahve them touching one another). If you put two in series the resistance doubles, if you put them in parallel you cut the resistance. I would suggest you keep adding 160K?? (Did you mean 16K?) resistors in series until the Open Lamp Protection (OLP) shuts down the inverter.

    Somewhere recently noted that using a .01 uF capacitor will also work, and there is little heat dissipation.

    PlainBill
    For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

    Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

    Comment


      #3
      Re: Faking CCFL inverter

      Hey Bill thanks for the reply. I had a typo, that was actually 130k 2watt resistors, not 160k, sorry. Just had them lying around and since two in series was close to the 200K you had mentioned earlyer I thought I would give em a try. So I think I will try adding the other two for a total of 4 in series to see the result, more like seeing if the heat dissapation is better. I will let you guys know later. I then should have 8 watts in series if I read your answer correctly.

      I tried soldering some new lamps in place of the old ones, but when I tried putting the diplay back together, the new lamps broke and what a disaster. Those displays are packed tighter than a drum and are hard to get back together the way they came from the factory. Mine are the HDS190MEN3 displays made by Hannspree and fit in the Optiplex Q91b and the Hanns G HX191D 19" monitos. I think there are even some in 19" Viewsonics as well.

      Oh Well, back to the drawing board.

      Tripp

      Comment


        #4
        Re: Faking CCFL inverter

        Originally posted by PlainBill View Post
        Somewhere recently noted that using a .01 uF capacitor will also work, and there is little heat dissipation.
        That would be this thread ...

        https://www.badcaps.net/forum/showthread.php?t=13713

        If the above works, post pictures of the modification.
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        Comment


          #5
          Re: Faking CCFL inverter

          Agree with retired, I will be glad if a photo can be shared.

          Inspired by the success of that thread, I went to the local store & bought a few ceramic 0.01uf 1kV caps.

          I had previously bought a faulty HP 1907w monitor (backlight shutting off after 30-40 mins) and found that by substituting a spare CCFL on one of 4 CCFL it will make it work again (only 1 out of the 4 is faulty) without much difference in brightness. So I thought, well, maybe I can just solder the ceramic caps across it as per THAT thread. So I soldered at the bottom as in the photo attached (note that I used another PSU board just as reference). However, it was unsuccessful. The moment I plugged it, it became 2-sec-to-black problem. I swapped the ceramic cap with a 200kohms 2W, but the result is the same.

          Am I soldering at the right location? Or must I solder from the top side (the leads in the socket)?..
          Attached Files

          Comment


            #6
            Re: Faking CCFL inverter

            Originally posted by newbie1 View Post
            I had previously bought a faulty HP 1907w monitor (backlight shutting off after 30-40 mins) and found that by substituting a spare CCFL on one of 4 CCFL it will make it work again (only 1 out of the 4 is faulty) without much difference in brightness. So I thought, well, maybe I can just solder the ceramic caps across it as per THAT thread. So I soldered at the bottom as in the photo attached (note that I used another PSU board just as reference). However, it was unsuccessful. The moment I plugged it, it became 2-sec-to-black problem. I swapped the ceramic cap with a 200kohms 2W, but the result is the same.

            Am I soldering at the right location? Or must I solder from the top side (the leads in the socket)?..
            I really think it depends on the design and how sensitive the safety portion of the CCFL circuitry is.
            After a lot of experimentation I have had better quicker or better results by substituting two lamps at a time.And then check to make sure the lamps stay on before you assemble completely.
            I am not a wagering type of person, But if I was, you're going to find at least one of the CCFL return wires has burned or come loose. And most likely a little solder will fix you problem.
            The hardest thing on the 1907 is getting the case apart.Disassembling the LCD panel is easy.
            Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

            Comment


              #7
              Re: Faking CCFL inverter

              It is hard for me to tell from the picture but if I was going to solder directly to the inverter I would make sure it is the two solder pads that are soldered to the two output pins that the lamps plug into. Both of my lamps were bad on the bottom of my HSD190MEN3. The lamps were both broke in half close to the solder points of the input wires.But what I am doing is using the wires from the bad lamps to put my resitors to and then just plug that into the inverter. If I can get this to work and work safely I will post pictures. The Capacitor thing is interesting too and I want to try that as well.

              Comment


                #8
                Re: Faking CCFL inverter

                Originally posted by PlainBill View Post
                Somewhere recently noted that using a .01 uF capacitor will also work, and there is little heat dissipation.
                That power has to go somewhere, most likely the coils in the transformer.

                Comment


                  #9
                  Re: Faking CCFL inverter

                  On researching some other issue, I came across this document describing a test set up for CCFL inverters, and remembered this thread. I don't know if this would be a universal tester, but they describes using a 110k 10w resistor as a dummy load. I haven't found such a resistor, but I will pick up a 47k + 33k + 2x15k 11w resistors next week to test.

                  I'm enclosing a pdf version of the document, in case the one linked to disappears.

                  Edit: The pdf didn't take.
                  Attached Files
                  Last edited by sofTest; 08-20-2011, 11:27 PM.
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