Vizio M420NV no backlight

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • jman100
    New Member
    • Aug 2016
    • 5
    • United States

    #1

    Vizio M420NV no backlight

    Hi guys,

    Looking for some advice on a Vizio M420NV. The screen comes on and the tv functions fine, audio and video, but the backlight is completely out. I was only able to tell the picture was still there by holding up a flashlight to it.

    There is never any flicker at all from the LEDs, they completely do not come on. I'm a novice on hardware stuff so any advice on what to test is appreciated. I looked for a BL_ON pin but I cannot find one labeled that, and don't know what it would look like.

    Thanks in advance!
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: Vizio M420NV no backlight

    We need good clear pictures of the whole backside of the TV showing all the boards, and then pictures of each board.
    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

    • jman100
      New Member
      • Aug 2016
      • 5
      • United States

      #3
      Re: Vizio M420NV no backlight

      Sorry for the delay, here are a bunch of pics.
      Attached Files

      Comment

      • CapLeaker
        Leaking Member
        • Dec 2014
        • 8066
        • Canada

        #4
        Re: Vizio M420NV no backlight

        turn the tv on and check the DC V on the BLon pin.

        Comment

        • jman100
          New Member
          • Aug 2016
          • 5
          • United States

          #5
          Re: Vizio M420NV no backlight

          Originally posted by CapLeaker
          turn the tv on and check the DC V on the BLon pin.
          Once again sorry for the delay.

          BL_ON shows .03 volts while the tv is off, and goes to .12 when the tv is turned on.

          Comment

          • CapLeaker
            Leaking Member
            • Dec 2014
            • 8066
            • Canada

            #6
            Re: Vizio M420NV no backlight

            That sux. Main board isn't sending BLon signal...
            since the tv comes on and the backlights stay off, it's a bad EEPROM on the main board.
            Your choices are to get a new replacement main board, or buy the repair kit at Shopjimmy for your board number 0171-2272-3174. You would have to change 2 two ICs (U14 and U33) on the main board. U14 fixes the frozen on welcome screen, U33 is for the backlights.
            Last edited by CapLeaker; 08-28-2016, 08:35 PM.

            Comment

            • jman100
              New Member
              • Aug 2016
              • 5
              • United States

              #7
              Re: Vizio M420NV no backlight

              Originally posted by CapLeaker
              That sux. Main board isn't sending BLon signal...
              since the tv comes on and the backlights stay off, it's a bad EEPROM on the main board.
              Your choices are to get a new replacement main board, or buy the repair kit at Shopjimmy for your board number 0171-2272-3174. You would have to change 2 two ICs (U14 and U33) on the main board. U14 fixes the frozen on welcome screen, U33 is for the backlights.
              Darn. Oh well, I did acquire the TV for free. I might get the repair kit.

              I assume there's no way to bypass or manually try to turn the backlight on to make sure?

              Comment

              • CapLeaker
                Leaking Member
                • Dec 2014
                • 8066
                • Canada

                #8
                Re: Vizio M420NV no backlight

                To force the PSU on, only leave the backlights connected. Take two 1k ohm resistors and jump STBY voltage to PSon and STBY voltage to BLon. Plug it in and the backlights should be up. If not, try to put a third resistor between STBY and ADJ.

                Comment

                • sricechex
                  Member
                  • Mar 2018
                  • 17
                  • United States

                  #9
                  Re: Vizio M420NV no backlight

                  I know this was a while back, but I thought this may be a source for diagnosing an almost identical problem.
                  I have a m420nv with no backlight, good image, white logo.
                  VLED voltages of 164v.
                  BL_ON from 0.4v off to 0.8v on.
                  Does this sound like an eeprom failure on the main board?
                  Is there further diagnostic information necessary or suggested?

                  Thanks!

                  Comment

                  • nomoresonys
                    Badcaps Legend
                    • Jan 2013
                    • 12094
                    • U.S.

                    #10
                    Re: Vizio M420NV no backlight

                    Unplug tv, then unplug powersupply board from mainboard, plug tv back in turn tv on see if backlights come on, that will work if it has pull up resistors if not you have to do like CapLeaker instructs in post # 8.

                    Comment

                    • sricechex
                      Member
                      • Mar 2018
                      • 17
                      • United States

                      #11
                      Re: Vizio M420NV no backlight

                      Great! Thank you, nomoresonys. I'll give that a shot.

                      If I can confirm that the backlights can be forced on successfully, can I be relatively confident that there is an eeprom failure on the mainboard? (is there a source for ideal voltages at those signal pins?)

                      Comment

                      • nomoresonys
                        Badcaps Legend
                        • Jan 2013
                        • 12094
                        • U.S.

                        #12
                        Re: Vizio M420NV no backlight

                        As CapLeaker says in post 6, if you don't have ps_on coming from the mainboard, most likely a mainboard fault, you could try heating the mainboard a little with a hair dryer, see if it trys to come on or anything changes.

                        Comment

                        • sricechex
                          Member
                          • Mar 2018
                          • 17
                          • United States

                          #13
                          Re: Vizio M420NV no backlight

                          I think he was taking about BL_ON , Not PS_ON?
                          That certainly makes sense, I'm just inexperienced as to what voltage constitutes "getting no signal. "
                          I'm getting 0.8v, but should it be a known board signal voltage like 3.2 or 5v?

                          Comment

                          • nomoresonys
                            Badcaps Legend
                            • Jan 2013
                            • 12094
                            • U.S.

                            #14
                            Re: Vizio M420NV no backlight

                            http://www.shopjimmy.com/vizio-3642-...for-m420nv.htm The board is 134 bucks there but they have eprom kits for around 20.

                            Comment

                            • nomoresonys
                              Badcaps Legend
                              • Jan 2013
                              • 12094
                              • U.S.

                              #15
                              Re: Vizio M420NV no backlight

                              https://www.ebay.com/itm/Vizio-3642-...ty!43616!US!-1
                              One there for 80 bucks, looks like these boards are pretty costly.

                              Comment

                              • nomoresonys
                                Badcaps Legend
                                • Jan 2013
                                • 12094
                                • U.S.

                                #16
                                Re: Vizio M420NV no backlight

                                Originally posted by sricechex
                                I think he was taking about BL_ON , Not PS_ON?
                                That certainly makes sense, I'm just inexperienced as to what voltage constitutes "getting no signal. "
                                I'm getting 0.8v, but should it be a known board signal voltage like 3.2 or 5v?
                                My bad I meant to say BL-ON.Yes I would expect about 3 or so. budm usually says 2.5 or greater equals backlights on and if I recall 1. or lower equals backlights off, something like that.
                                Last edited by nomoresonys; 03-21-2018, 06:18 PM.

                                Comment

                                • nomoresonys
                                  Badcaps Legend
                                  • Jan 2013
                                  • 12094
                                  • U.S.

                                  #17
                                  Re: Vizio M420NV no backlight

                                  Originally posted by sricechex
                                  I think he was taking about BL_ON , Not PS_ON?
                                  That certainly makes sense, I'm just inexperienced as to what voltage constitutes "getting no signal. "
                                  I'm getting 0.8v, but should it be a known board signal voltage like 3.2 or 5v?
                                  Yes usually around 3, you are way low there.
                                  Last edited by nomoresonys; 03-21-2018, 06:04 PM.

                                  Comment

                                  • sricechex
                                    Member
                                    • Mar 2018
                                    • 17
                                    • United States

                                    #18
                                    Re: Vizio M420NV no backlight

                                    If the backlights do work when forced, I'll give the eeprom-swap a try. I'll report relevant information as I find it.
                                    Is the standby voltage what should be expected in a live signal?

                                    Comment

                                    • nomoresonys
                                      Badcaps Legend
                                      • Jan 2013
                                      • 12094
                                      • U.S.

                                      #19
                                      Re: Vizio M420NV no backlight

                                      Did you try test in post #10.
                                      Last edited by nomoresonys; 03-21-2018, 05:59 PM.

                                      Comment

                                      • nomoresonys
                                        Badcaps Legend
                                        • Jan 2013
                                        • 12094
                                        • U.S.

                                        #20
                                        Re: Vizio M420NV no backlight

                                        https://www.youtube.com/watch?v=mUvclBfaMXg Testing powersupply by itself, unplug all other boards, he's using the ground pin for testing because he has board out of tv, you can just use the metal back of tv or other suitable ground for testing, IF you can't get a steady standby reading while testing with this methed, it's a powersupply board problem. Could try that to verify powersupply. CAREFUL HIGH VOLTAGE FROM THE HOT SIDE CAN BE DEADLY.

                                        Comment

                                        Related Topics

                                        Collapse

                                        • Tynan Dill
                                          Vizio e601i-A3 - Has Sound and Display, But No Backlight - Bad Power Supply Board or Bad LED Bulbs ?
                                          by Tynan Dill
                                          I was given this TV from my great uncle. He said it just wouldn't turn on one day out of nowhere, replaced the TV, and gave it to me to possibly fix and use for myself.

                                          Upon bringing it home and plugging it up, it showed a standby light.

                                          I powered it on and without a flashlight, the display showed the "V" but the lighting is very dim, but visible.

                                          The screen seems to blackout and stay black, but with a flashlight I can see the display.

                                          With my Playstation 4 connected via HDMI, and running a game I can hear sound.

                                          Assuming...
                                          11-22-2024, 01:46 PM
                                        • howardc64
                                          Vizio E55-F1 dark backlight zones. LED failure or Dimming Zone Driver?
                                          by howardc64
                                          Problem

                                          Fixing a dimming zone TV with LEDs not lighting up. Dimming zone circuit introduces added variable to diagnose LED and/or Dimming Zone Driver board? Some 1/2 rows of LEDs appears to be out in active dimming zone off AND some brightness flickering with active dimming zone high while playing changing video



                                          Model & Board Pics



                                          Conflicting Spec

                                          Vizio indicate this TV has 10 dimming zones. However, LED strips and Zoned light driver connector suggest 12

                                          https://www.shopjimmy.com/vizio-gj-2k1...
                                          10-10-2024, 01:16 PM
                                        • triplefour
                                          UN65TU700DF picture and sound but no backlight. BL tests ok but repl. PSU didnt fix!
                                          by triplefour
                                          this tv is throwing me for a loop. do samsung tvs no longer have the backlight self test feature built into the power supply?
                                          i tested the backlight with my LED tester and it lights up both strips. one of them reads 100v and the other reads 63.7v.
                                          unplugged mainboard from power supply but left backlight plugged in, and then plugged psu wall power in. expected to see backlights light up but see nothing.
                                          according to how ive diagnosed in the past, this would almost always be a bad power supply. replacement power supply was cheap like 20$ from ebay. but still i get not even...
                                          09-13-2023, 10:43 PM
                                        • JaquesPratt
                                          Vizio D32f-E1 Powers on, has backlight, won't boot/no logo, no menu or video
                                          by JaquesPratt
                                          I have a Vizio D32f-E1 LCD TV that does NOT have a TCON board.

                                          This TV recently went through some 'death throes' and now won't boot. The first problem that began to manifest was while watching tv, the screen would 'freeze', and the image would dim over a few seconds until it was very dark. HOWEVER, the audio of the show would continue as normal. I could power off the TV for 5-20 seconds, power back on, and the video would be normal. This would occur 1-3 times when the TV was first started, and would not happen again after the TV was 'warmed up'. Not ideal, but this glitch was manageable....
                                          07-16-2024, 01:04 AM
                                        • Mectronik
                                          Vizio m601d-a3 backlight issue
                                          by Mectronik
                                          Hello, I'm working on a Vizio m601d-a3 with a backlight issue that I am having a difficulty diagnosing it. As it sits, the tv powers on, displays the Vizio symbol and with nothing hooked up it will then display no signal but you can only see half of the screen. I know it's a back light issue because the picture is there without light behind it, as I can see it by doing a light test. I've taken off the paneling and done a visual inspection. If I disconnect the tcon ribbon cable to the affected side then the entire half of the screen goes away. I've checked voltages at the LED driver from the main...
                                          11-05-2023, 10:20 PM
                                        • Loading...
                                        • No more items.
                                        Working...