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    #61
    Re: Toshiba 49L621U

    Originally posted by jostewcrew View Post
    backlight flash on with toshiba logo, then went black with red led flashing 5 times. leds were good

    How did you confirm the LEDs were good? Backlight flash is usually a sign of bad LEDs. Do you have a LED tester? A few of the Toshibas I worked on had bad LEDs that damaged the LED controller on the power supply. The cost of replacing both was close to the value of the TV.

    Comment


      #62
      Re: Toshiba 49L621U

      to preface: after reconnecting pin 15 (dim) the set still continues to function properly. any reason? reset, something short close or open? did continuity between the wire at connector insert and the backside of the connector adapter itself to verify its actually back installed.

      1) So what do you have on DIM pin if all cables are put back in place?
      when the unit is off it jumps between 0v and -.1mv

      2) What DCV do yo have on the LED connector of EACH pins when you first turn on the TV (you will need to leave the meter probes in place, black probe on chassis, red probe on each LED connector) and then after 10 seconds then turn the TV off, so you have to repeat this test on each pin of the connector that has the wire connected to it, you also need to provide the pin name so we can easily see what it has or does not have..

      placed in min/max mode: p803 on power board (connector going to led strips)

      with led load:

      pin 1 vled1- = 15.6v
      pin 2 nc
      pin 3 vled2- = 17.1v
      pin 4 nc
      pin 5 vled3- = 15.3v
      pin 6 nc
      pin 7 nc
      pin 8 nc
      pin 9 nc
      pin 10 nc
      pin 11 vled+ = 97.4v
      pin 12 vled+ = 97.1v
      pin 13 vled+ = 97.3v

      without led load:

      pin 1 vled1- = 0v
      pin 2 nc
      pin 3 vled2- = 0v
      pin 4 nc
      pin 5 vled3- = 0v
      pin 6 nc
      pin 7 nc
      pin 8 nc
      pin 9 nc
      pin 10 nc
      pin 11 vled+ = 133.9v
      pin 12 vled+ = 134.3v
      pin 13 vled+ = 131.1v
      Attached Files
      Last edited by jostewcrew; 06-21-2020, 07:24 PM.

      Comment


        #63
        Re: Toshiba 49L621U

        Originally posted by neilc6 View Post
        How did you confirm the LEDs were good? Backlight flash is usually a sign of bad LEDs. Do you have a LED tester? A few of the Toshibas I worked on had bad LEDs that damaged the LED controller on the power supply. The cost of replacing both was close to the value of the TV.
        i first used my backlight tester to test voltages on all 3 strip circuits. they seemed within range of eachother and not off enough to indicate one of the leds went out. i opened it up to visually check each strip after replacing the power board, main board and tcon board without it resolving the issue.

        Comment


          #64
          Re: Toshiba 49L621U

          i understand that now with the unit functioning (havnt tested the led dim function as of yet) that some may not want to continue to theorize or such. im learning so im still curious as to why its working now after disconnecting/ reconnecting dim (pin 15)? im assuming its some type of variable resistor ..which i believe would have to be an ic of some sort to be able to increase/ decrease voltage for backlight dimming functionality? budms' insight provided me that it is controlled via the main board...id be interested in figuring out which component that would be and do some testing.
          Last edited by jostewcrew; 06-21-2020, 07:35 PM.

          Comment


            #65
            Re: Toshiba 49L621U

            It is PWM Dimming control. not variable resistor. You do know what PWM is, correct?
            You should check the dimming DCV reading when backlights stay on, it will be average reading since it is PWM not steady DC.
            BTW, LED tester only puts out about 30 mA instead of 200 ~ 300mA of operating current, so using tester will tell you if you have open circuit or not without having to disassemble the LCD panel, not for verify that the LED is good since bad LED will fail at operating current.
            Never stop learning
            Basic LCD TV and Monitor troubleshooting guides.
            http://www.badcaps.net/forum/showthr...956#post305956

            Voltage Regulator (LDO) testing:
            http://www.badcaps.net/forum/showthr...999#post300999

            Inverter testing using old CFL:
            http://www.badcaps.net/forum/showthr...er+testing+cfl

            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
            http://s807.photobucket.com/user/budm/library/

            TV Factory reset codes listing:
            http://www.badcaps.net/forum/showthread.php?t=24809

            Comment


              #66
              Re: Toshiba 49L621U

              It is PWM Dimming control. not variable resistor. You do know what PWM is, correct?

              i do not sir...link to good reading? iw ill google it after this message. im assuming by abbreviation pwr managmnt chip?

              You should check the dimming DCV reading when backlights stay on, it will be average reading since it is PWM not steady DC.

              with the unit on pin 15 (dim) is jumping between 3.005v and 3.024v

              BTW, LED tester only puts out about 30 mA instead of 200 ~ 300mA of operating current, so using tester will tell you if you have open circuit or not without having to disassemble the LCD panel, not for verify that the LED is good since bad LED will fail at operating current.

              im still familiarizing myself with the tools of the trade. this is good insight on the usage of this device. ive been using it to see only if any voltage reading differs when a circuit of led strips is tested. if they are all lighting and not greater than 3v apart, id say they are good (although sometimes i am unsure of myself so i open up anyway) but if one circuit doesnt light....automatic bulb/circuit failure to me. if one circuit differs between 3v and upwards and the other two are the same...i assume one or more bulbs are out (basing around 3v per bulb)

              Comment


                #67
                Re: Toshiba 49L621U

                https://www.analog.com/en/technical-...d-dimming.html

                https://focuslcds.com/journals/pwm-d...ight-for-lcds/

                "with the unit on pin 15 (dim) is jumping between 3.005v and 3.024v" that is fine.
                What is your TV LCD panel model number?
                Last edited by budm; 06-21-2020, 08:29 PM.
                Never stop learning
                Basic LCD TV and Monitor troubleshooting guides.
                http://www.badcaps.net/forum/showthr...956#post305956

                Voltage Regulator (LDO) testing:
                http://www.badcaps.net/forum/showthr...999#post300999

                Inverter testing using old CFL:
                http://www.badcaps.net/forum/showthr...er+testing+cfl

                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                http://s807.photobucket.com/user/budm/library/

                TV Factory reset codes listing:
                http://www.badcaps.net/forum/showthread.php?t=24809

                Comment


                  #68
                  Re: Toshiba 49L621U

                  pulse width modulator lol....not even close. i guess this is why techs use oscilloscopes? ill research this some more.

                  Comment


                    #69
                    Re: Toshiba 49L621U

                    What is your TV LCD panel model number?

                    is this the display unit part number itself? if not then the prefixes...(this may be what youre talking about) is: LTM7UCAR
                    Last edited by jostewcrew; 06-21-2020, 08:31 PM.

                    Comment


                      #70
                      Re: Toshiba 49L621U

                      There should be a sticker right on the back of the LCD panel.
                      Never stop learning
                      Basic LCD TV and Monitor troubleshooting guides.
                      http://www.badcaps.net/forum/showthr...956#post305956

                      Voltage Regulator (LDO) testing:
                      http://www.badcaps.net/forum/showthr...999#post300999

                      Inverter testing using old CFL:
                      http://www.badcaps.net/forum/showthr...er+testing+cfl

                      Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                      http://s807.photobucket.com/user/budm/library/

                      TV Factory reset codes listing:
                      http://www.badcaps.net/forum/showthread.php?t=24809

                      Comment


                        #71
                        Re: Toshiba 49L621U

                        Post # 4 show the LCD panel sticker, since there are more than on revision of this TV we do not know what LCD panel is used in your TV.
                        Never stop learning
                        Basic LCD TV and Monitor troubleshooting guides.
                        http://www.badcaps.net/forum/showthr...956#post305956

                        Voltage Regulator (LDO) testing:
                        http://www.badcaps.net/forum/showthr...999#post300999

                        Inverter testing using old CFL:
                        http://www.badcaps.net/forum/showthr...er+testing+cfl

                        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                        http://s807.photobucket.com/user/budm/library/

                        TV Factory reset codes listing:
                        http://www.badcaps.net/forum/showthread.php?t=24809

                        Comment


                          #72
                          Re: Toshiba 49L621U

                          Originally posted by budm View Post
                          Post # 4 show the LCD panel sticker, since there are more than on revision of this TV we do not know what LCD panel is used in your TV.
                          one sec...going to take a pic it is rev A
                          Attached Files
                          Last edited by jostewcrew; 06-21-2020, 08:49 PM.

                          Comment


                            #73
                            Re: Toshiba 49L621U

                            You have the same LCD panel as the OP, K490WDR1.
                            I cannot find the spec sheet for this model, the spec sheet will explain what the control signals requirement will be.
                            But at this point you do have reference Voltages of the working condition so just have to make measurement when it stops working.
                            Also try turning down the backlights level (not brightness) to as low as possible in the USER OSD to see if the TV will stay working longer.
                            Last edited by budm; 06-21-2020, 08:56 PM.
                            Never stop learning
                            Basic LCD TV and Monitor troubleshooting guides.
                            http://www.badcaps.net/forum/showthr...956#post305956

                            Voltage Regulator (LDO) testing:
                            http://www.badcaps.net/forum/showthr...999#post300999

                            Inverter testing using old CFL:
                            http://www.badcaps.net/forum/showthr...er+testing+cfl

                            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                            http://s807.photobucket.com/user/budm/library/

                            TV Factory reset codes listing:
                            http://www.badcaps.net/forum/showthread.php?t=24809

                            Comment


                              #74
                              Re: Toshiba 49L621U

                              Originally posted by budm View Post
                              You have the same LCD panel as the OP, K490WDR1.
                              I cannot find the spec sheet for this model, the spec sheet will explain what the control signals requirement will be.
                              no problem....for knowledge...what is the search terms you use to find these and what would it mean to me if i had this information?

                              Comment


                                #75
                                Re: Toshiba 49L621U

                                I just search by model number for the spec sheet.
                                Example of the LCD panel LC500DUE-SFR1 spec sheet.
                                This one tell you the spec and the requirement for driving the LED.s
                                Attached Files
                                Last edited by budm; 06-21-2020, 09:07 PM.
                                Never stop learning
                                Basic LCD TV and Monitor troubleshooting guides.
                                http://www.badcaps.net/forum/showthr...956#post305956

                                Voltage Regulator (LDO) testing:
                                http://www.badcaps.net/forum/showthr...999#post300999

                                Inverter testing using old CFL:
                                http://www.badcaps.net/forum/showthr...er+testing+cfl

                                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                http://s807.photobucket.com/user/budm/library/

                                TV Factory reset codes listing:
                                http://www.badcaps.net/forum/showthread.php?t=24809

                                Comment


                                  #76
                                  Re: Toshiba 49L621U

                                  Originally posted by budm View Post
                                  I just search by model number for the spec sheet.
                                  so that number is pulling up led strips for this model. im assuming the types of leds used ant the voltage requirements per bulb/strip/circuit would dictate the variable adjustment by the pwm?

                                  its obvious i need to start reading up. ty for the help and guidance. if it goes out again, ill know where to start. on a side note: im still curious as to why the new main board did not fix the issue being that its on the main board? or is it just controlled there but a part of something else?
                                  Last edited by jostewcrew; 06-21-2020, 09:07 PM.

                                  Comment


                                    #77
                                    Re: Toshiba 49L621U

                                    See post #75
                                    You need the spec sheet of the panel to know what the LEDs can be driven with.
                                    Last edited by budm; 06-21-2020, 09:09 PM.
                                    Never stop learning
                                    Basic LCD TV and Monitor troubleshooting guides.
                                    http://www.badcaps.net/forum/showthr...956#post305956

                                    Voltage Regulator (LDO) testing:
                                    http://www.badcaps.net/forum/showthr...999#post300999

                                    Inverter testing using old CFL:
                                    http://www.badcaps.net/forum/showthr...er+testing+cfl

                                    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                    http://s807.photobucket.com/user/budm/library/

                                    TV Factory reset codes listing:
                                    http://www.badcaps.net/forum/showthread.php?t=24809

                                    Comment


                                      #78
                                      Re: Toshiba 49L621U

                                      ill admit that this is a bit over my head as for now. i will continue to read on this and im sure it will click at my look back at the exapmles given. ty again. last question before i start my own research on all this...... is the pwm hardware driven or software driven? im not sure if im asking this right but is it an operation setting that drives the pwm or is it based on its own creations internal mechanisms?

                                      Comment


                                        #79
                                        Re: Toshiba 49L621U

                                        I've experienced this model to have a common problem with backlight failure. LEDS come on for between 5 seconds and 5 minutes then BL shuts off but image remains on screen. LED strips test OK with LED tester, but fail under normal load. The way to find the one strip that is failing under load is to test each strip one at a time by plugging in a good know strip in the place of the one being tested. Once you find the failed strip, the BL stay on. (This can be a challenging diagnosis because sometimes two strips are drawing too much current and are causing the BL shutdown!)

                                        Only a matter of time until the next strip fails... I suggest starting with a whole new set.
                                        Last edited by jjanssen7; 06-23-2020, 01:53 AM.

                                        Comment


                                          #80
                                          Re: Toshiba 49L621U

                                          so ive read up on pwm and understand quite a bit more...thank you budm and all for the schooling. i still dont know why disconnecting pin 15 (dim solved the issue, other than it bypassed the pwm module...(ic, fet?) dont have the schematic for this to wrap my head around the circuit, but got the main board in based upon your guys' knowledge of the pwm originating from the processor on the board. works like a charm. thanks agian.

                                          Comment

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