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Sanyo DP42848 42" LCD TV: sound, but no picture

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    Sanyo DP42848 42" LCD TV: sound, but no picture

    Yesterday, out of the blue, our 42" Sanyo DP42848 LCD stopped working. No lighting strikes or anything, it just stopped working properly. It's out of warranty.

    When turned on, we see a black screen with the blue "HDMI1" input notification in the corner: the screen appears to be uniformly lit, so it sure looks like the LCD and backlighting are all working properly. A few seconds later, at the point where it would normally start showing video, the backlights turn off and sound comes on. If I shine a light in, it looks like the LCD is showing video, but it has no lighting. Sometimes, it just simply turns itself off, which might have been my troubleshooting triggering some other safety.

    I did a bunch of googling, followed troubleshooting steps posted by others in this forum and in the service manual one of you posted (thanks!!). I'll try to summarize here, but I'm kinda stumped at this point.

    No obvious burnt components on the PSU, mainboard or inverter boards, and no capacitors are bulging or leaking. The HV side of the inverter transformers looks ugly, but it's hard to tell if it's burnt or just resin.

    Power Supply: with cables unplugged, I measured 24V to one of the inverter boards and 5V to ground on CN2. I'm unable to measure 24V to the other inverter board or 12 or 24V on CN2, but I suspect it's because power is intentionally turned off when they're unplugged. I was able to measure 12V and 24V to ground on mainboard on solder points near K8B, so I'm pretty sure at this point the power supply is OK.

    Main board: While the TV is running (sound, etc.) I'm getting 5V on IC800 pin 32 consistantly. I've had difficulty measuring it on pin 23, at some times measuring 0V, 3.5V, and 5V, but finally was consistently measuring 5V when sound was on. Might have been my error reading a wrong pin, or might have been while the TV was in standby or some sort of limp mode.

    Inverter boards: only thing I've found so far is that the HV side of the transformer nearest the edge of the board has no continuity between terminals on either board. The inboard transformer on both sides does have continuity. I measured 0.2Ohms on the LV side of each transformer between 3-4, & 4-5, but open circuits between 2-3 and 6-7. All were consistently like this. Is this my the problem or is it a red herring? I've not yet tested voltages on the inverter boards with the TV turned on due to all the shielding in the way.

    What's my next step?
    Attached Files
    Last edited by sjfehr; 10-19-2012, 09:38 AM.

    #2
    Re: Sanyo DP42848 42" LCD TV: sound, but no picture

    Update: just reinstalled the 2nd inverter board without the cage to try to measure the output to the backlighting. And the damned TV just started working again! Crossing my fingers and hoping it was just a loose connector and the troubleshooting process corrected it. Also hoping I didn't fry my meter, as there was quite a bit of sparking and wierd things on the display...

    Odd, though, that the symptoms persisted through playing with the PSU, mainboard and 1st inverter. And started working when I reinstalled the 2nd inverter, all the connections of which were firm and I didn't mess with the pins at all like I did the one cable on the PSU. I'll keep an eye on it and see if it continues working & post back with an update.
    Last edited by sjfehr; 10-19-2012, 10:10 AM.

    Comment


      #3
      Re: Sanyo DP42848 42" LCD TV: sound, but no picture

      Never try to measure the high voltage output of the inverter transformer, it can be as high as 2500V which will blow your typical DMM input circuit, you will need AC high voltage probe.
      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


        #4
        Re: Sanyo DP42848 42" LCD TV: sound, but no picture

        Yeah, I counted the transformer windings and looked at the insulation, and figured it was operating somewhere in the 200-300V range. So, set my meter to 600V and... well... didn't give me useful data, but appears to still be working. Even if the voltage isn't that high, the frequency is likely well outside the range of this meter.

        Comment


          #5
          Re: Sanyo DP42848 42" LCD TV: sound, but no picture

          Originally posted by sjfehr View Post
          Update: just reinstalled the 2nd inverter board without the cage to try to measure the output to the backlighting. And the damned TV just started working again! Crossing my fingers and hoping it was just a loose connector and the troubleshooting process corrected it. Also hoping I didn't fry my meter, as there was quite a bit of sparking and wierd things on the display...

          Odd, though, that the symptoms persisted through playing with the PSU, mainboard and 1st inverter. And started working when I reinstalled the 2nd inverter, all the connections of which were firm and I didn't mess with the pins at all like I did the one cable on the PSU. I'll keep an eye on it and see if it continues working & post back with an update.
          This exact thing happened to me, bought a bravia which would switch off after a couple of seconds, took the inverters out to see if anything was wrong, couldnt find anything. Plugged everything back in and its still working months after, switched on most of the day too with cbeebies on
          Do NOT touch heatsinks when testing for voltages as they may be LIVE!

          Comment


            #6
            Re: Sanyo DP42848 42" LCD TV: sound, but no picture

            Well, it's gone black again. Same as before, though this time it shows a few seconds of video before going dark. Sound continues to play. What should I check next?

            Comment


              #7
              Re: Sanyo DP42848 42" LCD TV: sound, but no picture

              I would check the pin on the inverter board for 24v input, and the BL_ON (INV_ON, or ON/OFF) pins. Tell us what you are getting right now
              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


                #8
                Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                What is BL_ON? I'm getting 5V on IC800 pin18, and 5V on connector K8B pin 1, both of which indicate the inverters should be on.

                Comment


                  #9
                  Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                  BL_ON is the backlights on signal generated by the main board to turn on the backlights. I do not know what IC800 is or where it is at.
                  For the backlights to be on, the inverter board needs 24VDC for power and the BL_ON signal (>3VDC) to turn on the PWM IC which drives the Gates of the MOSFETs which will drive the inverter transformers which will produce high voltage to drive the CCFL's.
                  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


                    #10
                    Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                    Ah, that should have been obvious. IC800 is on the mainboard and was the first troubleshooting step in the service manual, btw.

                    I'm getting 24VDC on several pins on the invetrer boards, and 2.2-3.2VDC on several other pins, and 0V on the rest. Unfortunately, I have no way of knowing which pin is BL_ON.

                    Comment


                      #11
                      Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                      Can I see good clear pictures of the master and the slave inverter board around the connector?
                      Check that black surface mounted fuse close to the connector that looks like a SMD resistor to see if it shows open. Check all fuses of both boards.
                      Attached Files
                      Last edited by budm; 10-24-2012, 08:04 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


                        #12
                        Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                        The fuses near the connector on both inverter boards look good. I was able to identify and test two likely pins: BL_SW=3.3V and BL_ADJ=3.3V.
                        Attached Files

                        Comment


                          #13
                          Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                          BL_SW is the backlights on signal and it looks OK, >3VDC. It looks like the inverter boards are getting all the correct signals and power.
                          So right now do you still get the backlikgts to be on for seconds then the backlights turn off?
                          Last edited by budm; 10-24-2012, 08:32 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


                            #14
                            Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                            Yes, but the interval is shorter now; the backlights come on for only about 1 second before going out.

                            Comment


                              #15
                              Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                              Any final advice/things to check or board to replace before I give up and buy a new TV?

                              Comment


                                #16
                                Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                                2 seconds to black can be

                                a) bad caps
                                b) bad ccfls
                                c) bad ccfl wiring (especially the return wiring)
                                d) bad secondary windings on the inverter transformer

                                More details starting with post #19 at

                                https://www.badcaps.net/forum/showthread.php?t=10419
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                                  #17
                                  Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                                  Originally posted by sjfehr View Post
                                  I measured 0.2Ohms on the LV side of each transformer between 3-4, & 4-5, but open circuits between 2-3 and 6-7.
                                  You should be getting a reading on the secondary side and not open circuit. If you have a manual range multimeter, you might have to set it to 20K ohms as some secondaries will reading > 2K ohms.
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                                    #18
                                    Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                                    What is the part number of the inverter transformer?
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                                      #19
                                      Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                                      Thanks, retiredcaps! That 2-seconds to black page is great, too. Didn't think to check the FAQs on the computer display forum.

                                      I double-checked the transformer secondaries. Found the same thing on both inverter boards: the transformer closest to the center of the board is reading 0.2 Ohms across the secondary, and the other transformer reads open on both 200Ohm and 2kOhm scales. I filed down into good solder to ensure resin wasn't fouling the measurements; the solder joints appear good.

                                      All 4 inverter transformers have identical part#s, written in two rows:

                                      T51.0165.211 e5
                                      0815 709 S

                                      Ring a bell for manufacturer/source? No obvious manufacturerer information on it.

                                      Comment


                                        #20
                                        Re: Sanyo DP42848 42" LCD TV: sound, but no picture

                                        Originally posted by sjfehr View Post
                                        the transformer closest to the center of the board is reading 0.2 Ohms across the secondary, and the other transformer reads open on both 200Ohm and 2kOhm scales.
                                        As I mentioned in post #17, use the 20K (twenty thousand) scale and retest. 2K (two thousand) may be too low.
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