Samsung 240t no backlight

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • almoodie
    Senior Member
    • Jan 2010
    • 66

    #1

    Samsung 240t no backlight

    Samsung 240t 2003 vintage
    Uses a power adapter which provides 14V
    When I connect the power supply adapter and press the on button the monitor beeps and the power indicator lamp flashes every second or so. Backlight does not come on at all not even for an instant. Pressing any of the control buttons produces a beep but no other response. I have wiring diagrams which I downloaded.

    Opened it up, images attached.
    Small power board 3" x 1.5" (DC to DC) has 3 Samsung electrolytics, no bulging or leakage. Has 14V input and three ouputs:
    GND
    VOUT 5V as per specs
    SIG 26.6V no idea what this should be but it seems a strange voltage.

    Inverter board has 3 TMZ electrolytics 330 microF 35V 105C. From the different make and the solder joints on these caps I assume they have been replaced. Are these replacements quality caps with appropriate ESR, could they have failed again or should I look elsewhere.

    The logic board receives the 14V input from the power adapter and feeds it some how through a 15 cable connector, terminals as follows (terminal number/expected value/actual reading:
    1 GND
    2 BL_Control 0V
    3 GND
    4 BL_EN
    5 GND
    6 GND
    7 5V -14,4V
    8 GND 14.4V
    9 GND 9.39V
    10 14V -14.4V (negative)
    11 14V -14.4V (negative)
    12 14V -14.4V (negative)
    13 14V -14.4V (negative)
    14 14V -14.4V (negative)
    15 14V -14.4V (negative)

    I'm a bit lost. Why is the logic board feeding the inverter board -14.4V (negative) is that OK. Any help appreciated.
    Attached Files
  • almoodie
    Senior Member
    • Jan 2010
    • 66

    #2
    Re: Samsung 240t no backlight

    Here's a closeup of the power supply section of the logic board. Power adapter connects at blue arrow, 14V in. This board then outputs power to the inverter board through 15 wire connector, red arrow.

    Comment

    • almoodie
      Senior Member
      • Jan 2010
      • 66

      #3
      Re: Samsung 240t no backlight

      Originally posted by almoodie
      Here's a closeup of the power supply section of the logic board. Power adapter connects at blue arrow, 14V in. This board then outputs power to the inverter board through 15 wire connector, red arrow.
      Second attempt with image
      Attached Files

      Comment

      • Scenic
        o.O
        • Sep 2007
        • 2642
        • Germany

        #4
        Re: Samsung 240t no backlight

        i've got a SyncMaster 210T (basically the same unit, just 21" instead of 24")

        they don't display the usual "no signal" message when nothing's connected to them.
        try hooking it up to a computer, it may work just fine
        especially since mine does exactly the same things that you described in the first post.

        but check the PSU.. mine had the main switcher cooked beyond recognition..
        Check the primary cap and the smaller 50V (?) one near it.. mine were baked dry, which probably set the main switcher on fire... lol

        caps in the LCD itself are no problem on my unit as of yet, but i thought about replacing the few thru-hole lytics with polys some day..

        as my PSU brick was toast, i'm using a toshiba laptop brick with the same ratings instead. just had to hook up the original cable to it..


        edit: that beeping is normal for those monitors. gets kinda annoying after some time, cause the monitor always beeps when you push a button (or rather touch the buttons... as they're touch sensitive buttons..)
        Last edited by Scenic; 03-26-2010, 07:38 PM.

        Comment

        • Radio Fox
          Badcaps Veteran
          • Jan 2010
          • 281
          • UK

          #5
          Re: Samsung 240t no backlight

          Originally posted by almoodie
          ...The logic board receives the 14V input from the power adapter and feeds it some how through a 15 cable connector, terminals as follows (terminal number/expected value/actual reading:
          1 GND
          2 BL_Control 0V
          3 GND
          4 BL_EN
          5 GND
          6 GND
          7 5V -14,4V
          8 GND 14.4V
          9 GND 9.39V
          10 14V -14.4V (negative)
          11 14V -14.4V (negative)
          12 14V -14.4V (negative)
          13 14V -14.4V (negative)
          14 14V -14.4V (negative)
          15 14V -14.4V (negative)

          I'm a bit lost. Why is the logic board feeding the inverter board -14.4V (negative) is that OK. Any help appreciated.
          What puzzles me even more than the -14.4V, is why are you getting 2 different voltages on pins that should be GND?

          The circuit board usually connects all the GND connections together.
          ________________________________________________

          Invisible airwaves crackle with life
          Bright antennae bristle with the energy
          ________________________________________________

          Comment

          • Radio Fox
            Badcaps Veteran
            • Jan 2010
            • 281
            • UK

            #6
            Re: Samsung 240t no backlight

            As for the -14V. Have you measured the voltage polarity of the adapter?

            You haven't got the polarity reversed have you?
            ________________________________________________

            Invisible airwaves crackle with life
            Bright antennae bristle with the energy
            ________________________________________________

            Comment

            • almoodie
              Senior Member
              • Jan 2010
              • 66

              #7
              Re: Samsung 240t no backlight

              Originally posted by Scenic
              i've got a SyncMaster 210T (basically the same unit, just 21" instead of 24")

              they don't display the usual "no signal" message when nothing's connected to them.
              try hooking it up to a computer, it may work just fine
              especially since mine does exactly the same things that you described in the first post.

              but check the PSU.. mine had the main switcher cooked beyond recognition..
              Check the primary cap and the smaller 50V (?) one near it.. mine were baked dry, which probably set the main switcher on fire... lol

              caps in the LCD itself are no problem on my unit as of yet, but i thought about replacing the few thru-hole lytics with polys some day..

              as my PSU brick was toast, i'm using a toshiba laptop brick with the same ratings instead. just had to hook up the original cable to it..

              edit: that beeping is normal for those monitors. gets kinda annoying after some time, cause the monitor always beeps when you push a button (or rather touch the buttons... as they're touch sensitive buttons..)
              I have tried using an input from a computer into the VGA input but it makes no difference.

              I replaced these two caps, happened to have new caps to suit, but it makes no difference. This board, DC to DC, outputs 5V as per specs. Will however replace the other two caps when I get them from Digikey.

              Al Moodie.

              Comment

              • almoodie
                Senior Member
                • Jan 2010
                • 66

                #8
                Re: Samsung 240t no backlight

                Originally posted by Radio Fox
                What puzzles me even more than the -14.4V, is why are you getting 2 different voltages on pins that should be GND?

                The circuit board usually connects all the GND connections together.
                Agreed, but I checked my values again and they are the same. My only way to go at the moment is to replace the three electrolytics on the power section of the logic board, 3 @ 100 micoF 16V 105 C, when they arrive.

                Comment

                • almoodie
                  Senior Member
                  • Jan 2010
                  • 66

                  #9
                  Re: Samsung 240t no backlight

                  Originally posted by Radio Fox
                  As for the -14V. Have you measured the voltage polarity of the adapter?

                  You haven't got the polarity reversed have you?
                  Adapter is brand new and I have checked the input, it reads +14V at entry to the DC to DC inverter board.

                  There is no way to reverse the polarity of the adapter it is a 4 pin DIN plug that will only fit one way.

                  I will wait for my order from Digikey to arrive and complete the replacement of all electrolytic caps. Otherwise I can't see any burnt components or dry joints.

                  Comment

                  • Scenic
                    o.O
                    • Sep 2007
                    • 2642
                    • Germany

                    #10
                    Re: Samsung 240t no backlight

                    hmm.. i think i'm gonna hook mine up and check the voltages... if that helps..

                    Comment

                    • stignatious
                      New Member
                      • Apr 2010
                      • 1

                      #11
                      Re: Samsung 240t no backlight

                      any word on voltages for this monitor? I've got the same issues with a 210t
                      thanks

                      Comment

                      • pedro
                        Senior Member
                        • Dec 2009
                        • 199
                        • AUSTRALIA

                        #12
                        Re: Samsung 240t no backlight

                        Originally posted by almoodie
                        Samsung 240t 2003 vintage

                        The logic board receives the 14V input from the power adapter and feeds it some how through a 15 cable connector, terminals as follows (terminal number/expected value/actual reading:
                        1 GND
                        2 BL_Control 0V
                        3 GND
                        4 BL_EN
                        5 GND
                        6 GND
                        7 5V -14,4V
                        8 GND 14.4V
                        9 GND 9.39V
                        10 14V -14.4V (negative)
                        11 14V -14.4V (negative)
                        12 14V -14.4V (negative)
                        13 14V -14.4V (negative)
                        14 14V -14.4V (negative)
                        15 14V -14.4V (negative)

                        I'm a bit lost. Why is the logic board feeding the inverter board -14.4V (negative) is that OK. Any help appreciated.
                        Maybe just a DOH! moment?

                        Just eyeballed those with the order/readings reversed. Assuming you had your meter connected to what you thought was a ground pin (1) but was actually pin 15, you get the following:

                        1 GND 0V
                        2 BL_Control 0V
                        3 GND 0V
                        4 BL_EN 0V
                        5 GND 0V
                        6 GND 0V
                        7 5V -14,4V 5V
                        8 GND 14.4V 0V
                        9 GND 9.39V 0V
                        10 14V 14.4V
                        11 14V 14.4V
                        12 14V 14.4V
                        13 14V 14.4V
                        14 14V 14.4V
                        15 14V 14.4V

                        I hope I have transposed them all correctly, and you follow what I'm getting at.
                        Friends don't let friends buy Samsung ....

                        Comment

                        Related Topics

                        Collapse

                        • m1ch43lzm
                          HP Pavilion 15-eh Board DAG7HAMB8F0 - CPU throttling to 0.4GHz (PROCHOT_EXT) and black screen
                          by m1ch43lzm
                          Hi, this is my personal laptop, which the original board (lets call it Board A) blew up PU8700 (TPS51486), making a hole on the board, i had left the laptop at my desk one day with the battery fully charged and didn't touch it for a week, but when i tried to turn it on it didn't
                          Thought the battery was dead, so i plugged in the charger then tried to power on, the power LED blinked once, charged LED still orange, unplugged the charger, plugged in again and I noticed the "magic smoke" smell, so i unplugged the charger, removed the back cover and saw the blown IC (the "magic...
                          05-12-2025, 08:37 PM
                        • ohren
                          Upgrading a Samsung ue55nu7096u with logic board from an ue55ru7105k -- good idea?
                          by ohren
                          I hope this is the right forum to post in despite not technically being a repair, but still a question of swapping boards.

                          I thought I'd explore the possibility to upgrade an existing working Samsung ue55nu7096u with the logic board (and power board if needed) of a newer model (ue55ru7105k) of the same size and appearance (and resolution). The reason being I'd like the extra inputs of that board including component in, an extra HDMI port and bluetooth. Its panel is broken so I have no use for the board otherwise.

                          The models launched in 2018 and 2019 respectively....
                          09-08-2023, 05:24 PM
                        • C152Heavy
                          Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board
                          by C152Heavy
                          Samsung LN46C630K1F – Intermittent Backlight, BN44-00341B Power Board

                          Summary for TL-DR readers:
                          • Backlight is intermittent, may come on with TV boot or not. No flickering, never fails during TV on.
                          • Have obtained Samsung schematic & service documents - Can upload if helpful.
                          • Have read ALL applicable threads
                          • C1818 and CP820 replaced as low hanging fruit
                          • CN802 data taken for normal and failed BL operation. SUMMARY: Pin 2 - 5vDet = 3.52 @normal, 0.0 @BL fail. Pin 6 - EPWM = 1.631 @normal, 1.058 @BL fail.
                          • VCC pin (18) of PFC...
                          01-11-2023, 02:53 PM
                        • Document Archive
                          Samsung Galaxy Book 2 Notebook Specification for Upgrade or Repair
                          by Document Archive
                          This specification for the Samsung Galaxy Book 2 Notebook can be useful for upgrading or repairing a laptop that is not working. As a community we are working through our specifications to add valuable data like the Galaxy Book 2 boardview and Galaxy Book 2 schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant badcaps forum. Please note that we offer no warranties that any specification, datasheet, or download...
                          09-07-2024, 05:50 AM
                        • Nicktronic
                          Samsung Power Supply Board BN44-00874F
                          by Nicktronic
                          Hey everyone,

                          This power supply board is hard to find but there are repair kits available. This board had a blown fuse, FP801S, blown PFC MOSFET, QP802CS and ceramic cap, CP809. I replaced them with parts I already had and tested the rest of the parts that would've come in the repair kit and they were fine. I powered the board up on the bench expecting, in typical Samsung power supply board fashion, to see all my output voltages but, nothing. 0 volts on CNL801, CNM801 and CNT801. The only thing I have is 170vdc on the filter caps. No standby voltage either.

                          Anybody...
                          03-17-2025, 06:20 AM
                        • Loading...
                        • No more items.
                        Working...