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No picture and sound Samsung LCD LE40A656A1FXXU

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    #1

    No picture and sound Samsung LCD LE40A656A1FXXU

    Hi,

    I have Samsung LE40A656 lcd tv from 2009 with no picture or sound.

    When I switch it on with the rc, the power led blinks a few times and then the cool fan for the Tcon comes on. But there is no picture or sound.
    When I push on "on" the tv starts direct but I have to push on "off" several times to get it off. I can switch the tv on with te touch button on the bezel but not off. When I turn it on, I also hear a startup sound from the speaker.

    Sometimes the cool fan stops for a few seconds and then starts again. I don't now why that is, I dont think it is mechanical, the time is to short to measure the voltage on the fan.

    A few years ago I already replaced 4 caps on the power'supply because sometimes it would turn on. Now I replaced all te caps on the power supply, but no change. (exept the two high voltage caps)

    I measured the voltages on the power supply and I think they are okay but a little bit low. Is that a problem?

    I can force the backlight on with some pull up resistors and the mainboard disconnected. So I think the lamps are ok.

    I also checked the voltage regulators on the mainboard and they are okay.

    Because of the strange behaviore of the mainboard I think I replace the mainboard but I am not sure.

    Can someone help me to identify the problem?

    Below there is a list with the numbers of the boards and the voltages I
    measured.

    LE40A656A1FXXU
    Mainboard:SK10BN9402451DD27QS213651 (BN41-00974B)
    Powersupply: TH08BN4400197AAM5RD1H8307

    CNI 806

    12V=11.47V
    FB=0.0V
    FB=0.0V
    GND=0.0V
    GND=0.0V
    LD=10.7V
    LD=10.7V


    CNI 803

    pin1 Inverter on/off= 0.0V
    pin2 NC=3.47V?
    pin3 PWM DIM=0.08V
    pin4 GND=0.0V
    pin5 Det_5V=5.03V

    CN 801

    pin1 power on/off=3.64V
    pin2 Sync=4.77V
    pin3 Stb 5.3V=5.05V
    pin4 GND=0.0V
    pin5 GND=0.0V
    pin6 GND=0.0V
    pin7 13V=12.88V
    pin8 13V=12.88V
    pin9 GND=0.0V
    pin10 GND=0.0V
    pin11 GND=0.0V
    pin12 GND=0.0V
    pin13 5.3V=5.03V
    pin14 5.3V=5.03V
    pin15 5.3V=5.03V
    pin16 5.3V=5.03V
    pin17 GND=0.0V
    pin18 GND=0.0V
    pin19 13V=12.88V
    pin20 GND=0.0V
    pin21 13V=12.88V
    pin22 13V=12.88V
    pin23 NC
    pin24 NC
    Tags: None
    #2
    Re: No picture and sound Samsung LCD LE40A656A1FXXU

    Hi, that mainboard suffer from a well known fault, are those 4 EL.CO. 1000uF10v, 2 near, 2 under the metal shield, change them with good quality SMD caps, fo example
    Panasonic EEEFC1A102P, it's not an easy task, stay careful with the path that come away if prolonged heat is applied..
    first, if you want, try to heat them with hairdryer then switch on, if it starts ok, the are them...
    Last edited by Davi.p; 02-04-2017, 02:26 PM.

    Comment

      #3
      Re: No picture and sound Samsung LCD LE40A656A1FXXU

      Hi Davi.P
      The elco's you mentioned are not on my mainboard. see the listing.

      Mainboard SK10BN9402451DD27QS213651 (BN41-00974B)

      C1120 100 16J measured in circuit 167.1mf 0.14kohm ESR ??

      C1121 100 16J measured in circuit 96.7mf 0.14kohm ESR ??

      C1201 strange mesurement ??

      C2139 100 16J measured in circuit 98.68mf 1.5ohm ESR

      C2140 100 16J measured in circuit 100.8mf 1.4ohm ESR

      C2160 220 35T measured in circuit 224.3mf 0.4ohm ESR

      C3170 100 16J measured in circuit 105.8mf 1.1ohm ESR

      C3189 47 16J measured in circuit 56.63mf 0.9ohm ESR

      C6151_op 220 16V measured in circuit 226.8mf 0.69ohm ESR


      I did not do the heattest yet.

      Comment

        #4
        Re: No picture and sound Samsung LCD LE40A656A1FXXU

        Here's a photo of my mainboard.
        Any suggestions?
        Attached Files

        Comment

          #5
          Re: No picture and sound Samsung LCD LE40A656A1FXXU

          "A few years ago I already replaced 4 caps on the power'supply because sometimes it would turn on"
          not so good to replace only few, in theese brands when you have the chance to open it up replace always all the caps with good brand, if them has at least 5 years, not so easy to find the big ones, but at least change the low voltage ones...
          "I measured the voltages on the power supply and I think they are okay but a little bit low. Is that a problem?"
          surely not...
          i'm sorry i had wathced only a little picture before make my suggestion of the 1000uf caps, this one is an implemented version of the older Bordeaux plus..
          is not a cap problem now, but i think it was, and them had damaged something on the mainboard, more probably, it's not easy to troubleshoot a ma.bo., one can only trace lvds data to tcon i think, with oscilloscope, the best way is find another screen even cracked, not too much, to test a little the signal, is possible a tcon damage also..
          do you have tested only linear regulators on ma.bo.? switching ones?

          Comment

            #6
            Re: No picture and sound Samsung LCD LE40A656A1FXXU

            looking at those voltages, you don't have any back light signal coming from the main board.
            pin1 Inverter on/off= 0.0V

            Comment

              #7
              Re: No picture and sound Samsung LCD LE40A656A1FXXU

              Hi,
              I tested the linear voltage regulators on the mainboard. Are there also switching ones?

              Are there other checks I could do before I order a new mainboard?

              Do you have any advice on how to order a mainboard. (numbers etc.)

              On another forum someone advised me to de-solder the Eeprom and then test the tv because It could be corrupted. I will try that this week.

              Comment

                #8
                Re: No picture and sound Samsung LCD LE40A656A1FXXU

                To reset the EEPROM manually here are the steps (Do this at your own risk). I have done this many times before and had success.
                1. Identify the EEPROM IC (24CXX)
                2. Identify the Flash memory IC (25LXX)
                3. Identify on the EEPROM IC the SDA and VCC pins
                4. Connect a jumper across the SDA and VCC pins
                5. Power ON the TV and hold for 20-25 sec
                6. Break the jumper
                7. Power OFF the TV

                Powering ON the TV again should show a reset EEPROM.
                GOOD LUCK!!

                Comment

                  #9
                  Re: No picture and sound Samsung LCD LE40A656A1FXXU

                  You can try freezing the EEPROM with a can of air upside down, then turn the TV on. If that doesn't do anything, you are just better off to replace the main board, unless you just want to tinker around for educational purposes.

                  Comment

                    #10
                    Re: No picture and sound Samsung LCD LE40A656A1FXXU

                    Originally posted by Joop View Post
                    the power led blinks a few times

                    How many times does it actually flash?

                    Comment

                      #11
                      Re: No picture and sound Samsung LCD LE40A656A1FXXU

                      Hi Andrew, i have always read on Italian forum the resetting with sh.cir. pin SDA - SCL.. i have done it on 2 tv's, one have worked, the other no.. and Capleaker, the freezing have worked for you?

                      Test the voltage on theese 2 Caps:
                      Attached Files

                      Comment

                        #12
                        Re: No picture and sound Samsung LCD LE40A656A1FXXU

                        Hi,
                        I found the Eeprom its a S 24C SO.
                        Try to do a reset as you described but no luck.
                        The standby led stil blinks 5 times and then nothing.

                        I measured the the two caps.
                        Top cap on the picture: left 0 v on the right side 3.33 v
                        Bottom cap on the picture: left 1.29v on the right side 0v
                        What does that mean?

                        I also measured the voltage on the eeprom between Vss and Vcc its 3.30 v

                        Comment

                          #13
                          Re: No picture and sound Samsung LCD LE40A656A1FXXU

                          How do you have found the eeprom? It's always the bigger in memory, i think in yours will be a 24c256
                          voltages seems ok even if i don't have schematics, but 3,3v is normal for many chips, 1,2xv is for the cpu.. try to let it stay on for many seconds, then feel the cpu with finger if it gets very hot, if yes then a probable try have to be a reflow of the CPU/main graphic chip (bigger one)

                          Comment

                            #14
                            Re: No picture and sound Samsung LCD LE40A656A1FXXU

                            It was the only chip I found with 8 legs and 24C.
                            Today I bought a mainboard. I will let you know if it works.
                            Last edited by Joop; 02-08-2017, 03:39 PM.

                            Comment

                              #15
                              Re: No picture and sound Samsung LCD LE40A656A1FXXU

                              "It was the only chip I found with 8 legs and 24C. "
                              Is not the medic that says that marking begin with 24c, you have to check every marking of 4+4 pin ic (marked Uxxx on board) by datasheet, you see if is compatible 24c256 or near.. in every tv mainboard ther are at least 3 eeproms (apart the ones with SPI-flash)
                              Last edited by Davi.p; 02-08-2017, 04:15 PM.

                              Comment

                                #16
                                Re: No picture and sound Samsung LCD LE40A656A1FXXU

                                Originally posted by Davi.p View Post
                                Hi Andrew, i have always read on Italian forum the resetting with sh.cir. pin SDA - SCL.. i have done it on 2 tv's, one have worked, the other no.. and Capleaker, the freezing have worked for you?

                                Test the voltage on theese 2 Caps:
                                You have to short the SDA and VCC pins not the SCL pin. That SCL pin is not touched at all. Sometimes instead of stopping the signal using VCC shorting the SDL and Gnd pins work.
                                Or simply replace the EEPROM with a new empty one or worst case get another Main Bd.

                                Comment

                                  #17
                                  Re: No picture and sound Samsung LCD LE40A656A1FXXU

                                  Andrew, i have resetted a tv eeprom with short on sda-scl, you don't thrust me? Try...
                                  SDL doesn't exists..

                                  Comment

                                    #18
                                    Re: No picture and sound Samsung LCD LE40A656A1FXXU

                                    ive also shorted pins sda-scl pins 5 and 6 and its worked fine this is the video i used as a guide
                                    https://www.youtube.com/watch?v=DZnlD24fMwM

                                    Comment

                                      #19
                                      Re: No picture and sound Samsung LCD LE40A656A1FXXU

                                      I found another eeprom with 256K mem. It was the only one with 256K mem according to the data sheet ATMLH 830 2EB. Shorting the pins didn't help. On another forum someone said to desolder the eeprom and see if the tv works? Is that possible?
                                      Getting the replacement board Saturday.
                                      Hope it isn't the Tcon that is causing the fault.
                                      Will keep you guy's informed.

                                      Comment

                                        #20
                                        Re: No picture and sound Samsung LCD LE40A656A1FXXU

                                        Tell which pins you shorted.. is possible that shorting doesn't make difference, i don't think desoldering is ok but one can try, there's another method but is difficult for someone, connect it to pc via rs232 and using LUDIPIPO schematic for interface (with a battery instead, it consist of only 2 resistors) and ICprog for software..
                                        Last edited by Davi.p; 02-11-2017, 04:38 AM.

                                        Comment

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