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    Hitachi 55HDX99 Plasma Tries to turn on then shuts off

    Hey guys, recently I repaired a Hitachi 55HDX99 Plasma TV with help from you guys on this thread. https://www.badcaps.net/forum/showthread.php?t=75627
    The problem ended up being a shorted buffer IC on the upper buffer board.

    After the repair, the TV was working fine and we used it on and off for about 20hrs. However, the last time we were using it, the TV just turned off in the middle of watching a show. There was no power at all and the power button did nothing.

    Unplugging the TV and plugging it back in makes all the relays click and the power light starts flashing blue. After a couple flashes, a relay on the power board clicks and all power is cut. I tried disconnecting the upper and lower buffer boards one at a time to see if another chip had failed but this made no difference. The symptom is also different from the bad buffer chip.

    Unplugging the main power connector coming out of the power supply board causes the TV to stay on and I can use the soft power switch normally but obviously there is no display. There is also no power on any of the output pins on the power supply. I suspect this is some sort of fault protection on the power supply board kicking in due to there being no load.

    One thing that I found interesting is that there are 3 heatsinks on the power supply board that each have a voltage labelled on them. There is 5V, 11V and 90V. When the TV is powered up with the output connector disconnected, the 5V and 11V heatsinks both have the listed voltages present on them when measuring between the heatsink and the chassis. However, the 90V heatsink does not have any voltage on it. I don't know if this is significant or not.

    If anyone has any ideas on what to look at first I would appreciate it.
    canadaboy25

    -Sometimes the light at the end of a tunnel is an on-coming train

    #2
    Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

    Hey there - maybe transfer some of the photos from the original post over here?

    Would you please post a clear picture of the power board and and markings on it? Time to look up service manuals or at least pictures of this board from ShopJimmy.com

    I suspect you have at least a blown FET somewhere.

    Have you checked for shorts across the two and three terminal parts that are heat sinked? Be careful. Make sure the caps on that board are discharged first before you touch anything. I would recommend removing the power board and ohm'ing out the two/three pinned TO-220 parts that are attached to the heatsink first. You can easily do this by looking at the bottom of the board.

    Do this for the "hot" (AC) and "cold" (DC) sides of the board.

    Are all of the fuses good?
    Last edited by ngth82; 03-26-2020, 08:42 PM.
    -Thomas
    I'm a hardware engineer focused on networking equipment for my day job. I void warranties and fix consumer electronics for fun.

    Comment


      #3
      Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

      Originally posted by ngth82 View Post
      Hey there - maybe transfer some of the photos from the original post over here?

      Would you please post a clear picture of the power board and and markings on it? Time to look up service manuals or at least pictures of this board from ShopJimmy.com

      I suspect you have at least a blown FET somewhere.

      Have you checked for shorts across the two and three terminal parts that are heat sinked? Be careful. Make sure the caps on that board are discharged first before you touch anything. I would recommend removing the power board and ohm'ing out the two/three pinned TO-220 parts that are attached to the heatsink first. You can easily do this by looking at the bottom of the board.

      Do this for the "hot" (AC) and "cold" (DC) sides of the board.

      Are all of the fuses good?

      Sorry, I thought I did upload some pictures. Looks like they didn't attach. I downloaded the service manual for the TV but it doesn't have any board schematics in it which is a shame.

      I will do those tests on the power board and report back.

      Thanks
      Attached Files
      canadaboy25

      -Sometimes the light at the end of a tunnel is an on-coming train

      Comment


        #4
        Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

        You need to check the voltages on the plugs, not the heatsinks. Check if you have Vs voltage, You need to monitor this pin when the tv is first turned on because if there is a fault the voltage will be shut down.
        These hitachi's usually have a bad buffer board, I would disconnect the upper buffer from the Y-sus (You can leave the panel ribbons connected) and try the tv to see if you have a picture on the lower half of the screen.
        I doubt you have a power supply problem.
        Last edited by R_J; 03-27-2020, 12:40 PM.

        Comment


          #5
          Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

          Originally posted by ngth82 View Post
          I suspect you have at least a blown FET somewhere.

          Have you checked for shorts across the two and three terminal parts that are heat sinked? Be careful. Make sure the caps on that board are discharged first before you touch anything. I would recommend removing the power board and ohm'ing out the two/three pinned TO-220 parts that are attached to the heatsink first. You can easily do this by looking at the bottom of the board.

          Do this for the "hot" (AC) and "cold" (DC) sides of the board.

          Are all of the fuses good?
          I checked all of the packages attached to the heatsinks and no shorts. Also all of the fuses are good.


          Originally posted by R_J View Post
          You need to check the voltages on the plugs, not the heatsinks. Check if you have Vs voltage, You need to monitor this pin when the tv is first turned on because if there is a fault the voltage will be shut down.
          These hitachi's usually have a bad buffer board, I would disconnect the upper buffer from the Y-sus (You can leave the panel ribbons connected) and try the tv to see if you have a picture on the lower half of the screen.
          I doubt you have a power supply problem.
          I have attached some waveforms of the voltages at the plugs when the tv is being turned on. With the plug connected to the power supply I get the 5V rail but the 60V and 90V rails only get up to about 0.5V and stay there for a few seconds before the TV shuts off. When the plug is disconnected, the 60V and 90V rails behave exactly the same, however, I no longer get the 5V rail. With the plug disconnected, the TV will stay powered up until I turn it off. Doing this must trigger some failsafe because when I reconnect the plug, I still have no 5V rail and the TV stays on. After a long enough time it will go back to shutting itself down.

          I originally had a bad buffer board on this TV and the symptom was that the TV would stay on, but the screen wouldn't come on. Right now it just turns itself off which is a different symptom than with the bad buffer board. Just to rule it out I tried it with the upper board disconnected and then the lower board disconnected. Both times the symptoms were exactly the same and the voltages on the plug of the power supply were the same. It powers up, then as soon as it is about to fire up the actual screen, it shuts down. I am measuring the voltages at CN64 on the power supply board and have attached a page from the service manual specifying what those voltages should be.

          Since the power supply connects to the X-sus board and then the Y-sus board connects to that, I disconnected the power cable between the X and Y sus boards and it responds exactly the same as it does when the cable is disconnected right at the power supply. This seems to suggest to me that if it is not a power supply fault, then it must be on the Y-sus board.
          Attached Files
          Last edited by canadaboy25; 03-27-2020, 04:06 PM.
          canadaboy25

          -Sometimes the light at the end of a tunnel is an on-coming train

          Comment


            #6
            Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

            You can test the power supply by itself but you will need a load on the Vs output, you can use a 60watt incandescent lamp as a load and see if the supply stays up.
            If the Vs exceeds 101vdc the power supply will go into shutdown and will remain that way untill reset
            Attached Files
            Last edited by R_J; 03-27-2020, 06:27 PM.

            Comment


              #7
              Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

              Originally posted by R_J View Post
              You can test the power supply by itself but you will need a load on the Vs output, you can use a 60watt incandescent lamp as a load and see if the supply stays up.
              If the Vs exceeds 101vdc the power supply will go into shutdown and will remain that way untill reset
              I soldered two wires onto a 60W incandescent bulb and tested it again to ensure that the bulb was good. I connected the wires to one of the 90V pins and ground pins on the power supply connector. The bulb did not glow and the voltages responded exactly the same way as they did without the bulb. I tried it with the power supply plug connected and disconnected. In both cases the response was exactly the same as it was without the bulb. I don't see how the Vs voltage could be exceeding 101v as it never makes it above 1 volt on the oscilloscope.
              canadaboy25

              -Sometimes the light at the end of a tunnel is an on-coming train

              Comment


                #8
                Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                The Vs only has to hit 101v once, then the next time you try it you will get 0 volts.
                I will assume that PRI501 fuse is ok, if it is then it is likely the primary side of the Vs circuit is ok and that the drive is missing.
                Are you checking the power supply board in the tv or on the bench?
                Last edited by R_J; 03-27-2020, 08:02 PM.

                Comment


                  #9
                  Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                  Originally posted by R_J View Post
                  The Vs only has to hit 101v once, then the next time you try it you will get 0 volts.
                  I will assume that PRI501 fuse is ok, if it is then it is likely the primary side of the Vs circuit is ok and that the drive is missing.
                  Oh ok I understand what you mean. I thought you were referring to when I lose the 5V rail for a while after powering the TV up with the power supply disconnected. It takes about 5 mins of sitting for that to reset on it's own.

                  I will try following the steps that you posted to reset the supply.
                  canadaboy25

                  -Sometimes the light at the end of a tunnel is an on-coming train

                  Comment


                    #10
                    Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                    Are you checking the power supply on the bench or in the tv? if it is in the tv, I believe you need to disconnect CN68 for about 5 seconds, then re-connect it

                    Comment


                      #11
                      Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                      Originally posted by R_J View Post
                      Are you checking the power supply on the bench or in the tv? if it is in the tv, I believe you need to disconnect CN68 for about 5 seconds, then re-connect it
                      I am checking it in the TV with all other connectors still plugged into it. I wasn't sure if there were enable signals required for all of the rails to start up if it was on the bench.
                      canadaboy25

                      -Sometimes the light at the end of a tunnel is an on-coming train

                      Comment


                        #12
                        Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                        Yes you can check it on the bench, You need the lamp across the Vs to ground, Then connect (CN63 pin3 to 6&7), this gives the low voltage, You wil then also need to connect (CN68 pin9 to 2&3) this then gives the Vs voltage.

                        Comment


                          #13
                          Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                          Originally posted by R_J View Post
                          Yes you can check it on the bench, You need the lamp across the Vs to ground, Then connect (CN63 pin3 to 6&7), this gives the low voltage, You will then also need to connect (CN68 pin9 to 2&3) this then gives the Vs voltage.
                          Ok, so I took the power supply board and the little filter board with the ac jack on it out of the TV and to the bench. I connected pins 3,6,7 on CN63 together and pins 2,3,9 on CN68 together. I connected the light bulb across the 90V pins and ground pins on CN64 and also connected my multimeter across the light bulb.

                          I applied the power and got no voltage on the multimeter and no glow from the light bulb. Very shortly after the power was applied, the relays clicked and the power supply shut itself down.

                          I double checked that I had all the correct pins connected on the right connectors and everything was good. So I'm not sure why I'm not getting any voltage out of it.

                          I also followed the procedure you posted for testing the board in the TV and got the same results. All of the low voltages are present in the first test, but I have no Va or Vs voltages and the power supply shuts itself off very quickly. After disconnecting and reconnecting the jumpers, the power supply resets itself.
                          Last edited by canadaboy25; 03-27-2020, 10:48 PM.
                          canadaboy25

                          -Sometimes the light at the end of a tunnel is an on-coming train

                          Comment


                            #14
                            Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                            Are you getting a good PFC voltage? You can check it on PRI501 fuse, It should be around 395 volts
                            Also check the solder connections on T1501 & T1502
                            Last edited by R_J; 03-28-2020, 12:16 PM.

                            Comment


                              #15
                              Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                              Originally posted by R_J View Post
                              Are you getting a good PFC voltage? You can check it on PRI501 fuse, It should be around 395 volts
                              Also check the solder connections on T1501 & T1502
                              I tested the PFC voltage with the board in the TV and all the other connectors plugged in and I get 336V on that fuse the whole time the TV is on until it turns itself off. With CN64 disconnected so that the TV stays on until I shut it off, I get 336V the entire time the TV is on.

                              The solder joints on those two transformers looked fine but I reflowed them all with plenty of flux just to be sure. It had no effect on the symptoms.
                              canadaboy25

                              -Sometimes the light at the end of a tunnel is an on-coming train

                              Comment


                                #16
                                Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                                Have you checked that you have all the voltages on plug CNPPS, when ON
                                pins 1~3, +5.7v
                                pin 7, +10V
                                pin 9, +16V
                                pin 13~15, +12v
                                Pins 4,5,6,8,10,11,12 GND
                                Also that pfc voltage seems low, There could be a small fuse (PRI101) open.
                                Last edited by R_J; 03-28-2020, 06:03 PM.

                                Comment


                                  #17
                                  Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                                  Originally posted by R_J View Post
                                  Have you checked that you have all the voltages on plug CNPPS, when ON
                                  pins 1~3, +5.7v
                                  pin 7, +10V
                                  pin 9, +16V
                                  pin 13~15, +12v
                                  Pins 4,5,6,8,10,11,12 GND
                                  All of the voltages are present except pins 13-15 have 10.8V instead of 12V. On the test procedure you posted, it says pins 7,13,14,15 should have 10.7V which is what I am getting.
                                  Last edited by canadaboy25; 03-28-2020, 05:59 PM.
                                  canadaboy25

                                  -Sometimes the light at the end of a tunnel is an on-coming train

                                  Comment


                                    #18
                                    Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                                    They are correct, +10.7 is what they should read. there is very little information on these tv's. Did you check that PRI101 (thermal fuse) is ok. it is just for the pfc circuit.

                                    Comment


                                      #19
                                      Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                                      Originally posted by R_J View Post
                                      They are correct, +10.7 is what they should read. there is very little information on these tv's. Did you check that PRI101 (thermal fuse) is ok. it is just for the pfc circuit.
                                      Just checked it. The fuse is good.
                                      canadaboy25

                                      -Sometimes the light at the end of a tunnel is an on-coming train

                                      Comment


                                        #20
                                        Re: Hitachi 55HDX99 Plasma Tries to turn on then shuts off

                                        Is there a service manual somewhere that you got that test procedure from? It would be helpful to have a better service manual than the one I have.
                                        canadaboy25

                                        -Sometimes the light at the end of a tunnel is an on-coming train

                                        Comment

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