MODIS BackLight Repair

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  • BMWGUY
    Junior Member
    • Feb 2016
    • 8

    MODIS BackLight Repair

    Hello, I have repaired many MODIS CCFL back lights. The LT1786FCS Ic that controls current to the florescent inverter and the primary winding capacitor are the problem 99% of the time.

    The LT1786FCS receives info via the mother board SM bus.
    It then increases or decreases the current to the inverter.

    The SMDIC03680TB00KQ00 capacitor is on primary winding.
    If it is bad you can only get 1/2 the KV output needed.

    I always replace both at the same time.

    Here is a link to buy the Ic http://www.linear.com/product/LT1786F

    Here is a link to buy the capacitor http://www.mouser.com/ProductDetail/...IbFyINUMQIo%3d

    MODIS boards are soldered using re-flow method but these items can be replaced using low temp solder and a small electronics iron.

    Be careful removing the old Ic, heat all legs until it easily lifts.
    Do Not Pry It Loose! The printed board may peel up with the Ic.
    No Fixin That!

    I have attached a BMP of the circuit and a BMP to show locations.

    If you are not comfortable removing and soldering the Ic, most electronic repair stores will do the work if you have the parts.
    Hope this is helpful
    Attached Files
    Last edited by BMWGUY; 02-28-2016, 07:40 PM.
  • DerekLMartin
    Junior Member
    • Jul 2011
    • 4

    #2
    What sort of symptoms do you get when these components fail. My modis screen turns on and I can adjust brightness but doesn't go all that bright. Would this be my problem??

    Comment

    • BMWGUY
      Junior Member
      • Feb 2016
      • 8

      #3
      Backlight will usually adjust but only go to be about half the brightness with it adjusted up to full. I would try the cap first

      Comment

      • Bushytails
        Junior Member
        • Oct 2016
        • 2

        #4
        The SMDIC03680TB00KQ00 is a 0.68uF capacitor, but the typical application in the LT1786FCS datasheet shows a 0.068uF. Did you paste the wrong part number, or are you finding the much larger capacitor to be the right replacement? I checked an older MODIS where the capacitor was labeled, and it's a 104K, or 0.1uF. A 0.1uF replacement looks like it's SMDIC03100TA00KQ00.

        I need to get my 'scope out and actually diagnosis it before swapping parts, of course... I'm leaning slightly towards the ZDT1053 dual transistor based on the symptoms, but will look at the primary capacitor and control IC first based on your post. Backlight lights very dimly, and on just one end. Stays about the same brightness if you adjust the brightness settings, but goes off entirely if you set it to maximum brightness. Seen this set of symptoms before?

        Thanks,
        --Bushytails

        Comment

        • Bushytails
          Junior Member
          • Oct 2016
          • 2

          #5
          'scoped mine, signal from the control chip looked good, but the royer converter waveforms looked like ****. Decided the cap was open, and sure enough, a new .1uf fixed it.

          --Bushytails

          Comment

          • Dwayne209
            Junior Member
            • Sep 2017
            • 2

            #6
            Got a modis that is bright when plugged in to wall power but goes dark on battery power. The unit stays on, the screen just goes dark. would this IC be my problem....

            Thanks guys

            Comment

            • Dwayne209
              Junior Member
              • Sep 2017
              • 2

              #7
              Fixed it.... it was the capacitor listed above. Swapped one from an old board I had lying around. Thanks guys

              Comment

              • DerekLMartin
                Junior Member
                • Jul 2011
                • 4

                #8
                Can anyone confirm that the original post has the correct part number for the capacitor? I am about to purchase these parts to repair my screen but don't want to buy the wrong capacitor. I may have to tear mine apart and see if there is a part number on my old one.
                Thanks
                Derek

                Comment

                • BMWGUY
                  Junior Member
                  • Feb 2016
                  • 8

                  #9
                  The SMDIC03680TB00KQ00 0.68uF capacitor is the recommended part according to the manufacture of the IC driver chip. The diagram is from their site with notes added.

                  The Snap-On MODIS board uses SMDIC03100TA00KQ00 0.1uF capacitor.
                  I have used both and either works fine.
                  The SMDIC03100TA00KQ00 0.1uf capacitor is the correct direct replacment part and the best choice.

                  Comment

                  • matt_o_70
                    Junior Member
                    • Apr 2018
                    • 1

                    #10
                    Has anyone tried a LED backlight kit such as this:



                    Its not very cheap considering what it is but, I am just staring to look for replacement options and this was the first on I came across..

                    Comment

                    • arnoldtx
                      Junior Member
                      • Sep 2018
                      • 1

                      #11
                      Not finding the cap on the web for sale

                      Does anyone have a source for the capacitor?

                      Comment

                      • Witsend
                        Banned
                        • Nov 2012
                        • 2942

                        #12
                        No more Radio Shack, maybe try Digikey

                        Comment

                        • Igore
                          Junior Member
                          • Mar 2007
                          • 4

                          #13
                          : MODIS BackLight Repair Reply to Thread

                          Where did you find the diagrams? I can't even find a diagram for a 10 year old Kenmore refrigerator control panel.

                          Comment

                          • AnalogueFan
                            Junior Member
                            • Feb 2022
                            • 2

                            #14
                            LT1786FCS Availability - Small Quantity, Small Price?

                            I'm not having a lot of luck finding a small quantity (2-3) of the LT1786FCS chip even remotely close to the bulk price ($5.95/ea minimum of 50) at, say, Analog Devices or Mouser. Anybody know where I can find this chip for way less than hundreds of dollars for a small quantity of these?

                            Also, here https://www.analog.com/en/products/l...ct-discussions are two different LT1786FCSes (scroll down near bottom)--can I use either one?

                            BMWGuy, great thread, many thanks. My EEMS300 display is useable but not very bright.

                            Originally posted by BMWGUY
                            Hello, I have repaired many MODIS CCFL back lights. The LT1786FCS Ic that controls current to the florescent inverter and the primary winding capacitor are the problem 99% of the time.

                            The LT1786FCS receives info via the mother board SM bus.
                            It then increases or decreases the current to the inverter.

                            The SMDIC03680TB00KQ00 capacitor is on primary winding.
                            If it is bad you can only get 1/2 the KV output needed.

                            I always replace both at the same time.

                            Here is a link to buy the Ic http://www.linear.com/product/LT1786F

                            Here is a link to buy the capacitor http://www.mouser.com/ProductDetail/...IbFyINUMQIo%3d

                            Comment

                            • AnalogueFan
                              Junior Member
                              • Feb 2022
                              • 2

                              #15
                              BTW, just for general info, I got my capacitors at Mouser


                              Originally posted by arnoldtx
                              Does anyone have a source for the capacitor?

                              Comment

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