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Sharp LC-50UB30U. Completely dead, no power indicator.

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    #21
    Re: Sharp LC-50UB30U. Completely dead, no power indicator.

    Originally posted by R_J View Post
    Remember ALL voltages on the primary or HOT side use hot ground not chassis ground.
    Those voltages seem low, the ncp1608b startup threshold is 11 volts, this supply would come from Q601 emitter.
    It could be that C603 is weak, Can you make out the markings on ZD604?
    ZD604 if viewed sideways (pins East-West) under the microscope: ||||| DZ then W47 turned 90° CCW.
    Tested good in situ.

    C603: 22uF x 50v, 105°C, Nippon Chemi-Con, 21.2uF as measured.
    Replaced with a higher capacitance just in case, 33uF x 50v, 85°C, Matsushita, 31uF as measured.

    No difference.
    Last edited by HAHOMETP; 08-23-2020, 06:51 PM.

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      #22
      Re: Sharp LC-50UB30U. Completely dead, no power indicator.

      Originally posted by R_J View Post
      You may also want to check that D121A, D121B, D120A & D120B are ok and not shorted. Sometimes if one of the diodes short the pfc will not operate to full boosted voltage, this is not likely the issue but worth checking.
      At first I thought that the D121A, D121B, D120A & D120B were arranged in a bridge, but then again, why not use a dedicated bridge instead? After a closer look I see that the D121A and D121B are in series, whereas the D120A and D120B are parallel. Bizarre. Anyway, no shorts, and no open circuits, although in theory either the D120A or the D120B could be open and not show it in situ masked by the other diode. I seldom see blown power diodes except perhaps in automotive alternators. If need be I can desolder one pin of either the D120A or the D120B and test for open junction.

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        #23
        Re: Sharp LC-50UB30U. Completely dead, no power indicator.

        The zener will likely check ok, but the zener, being in the base of Q601 sets the emitter voltage, DZ could be a BZT52H-B18 which is a 18 volt zener, so the input to the collector should be around 20 volts for it to supply around 18 volts for the vcc to the other ic's
        Does it look like this E8 (which is a 39volt)
        Attached Files

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          #24
          Re: Sharp LC-50UB30U. Completely dead, no power indicator.

          Originally posted by R_J View Post
          Does it look like this E8 (which is a 39volt)
          Yep, 1:1.

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            #25
            Re: Sharp LC-50UB30U. Completely dead, no power indicator.

            Well it's the standby transformer that supplies that voltage, R606a,b are just low ohm resistors (acting like fuses) D603 is the rectifier diode for the voltage and C603 is the filter. What is the voltage across C603 in standby? It could be that ZD604 is bad and zenering at the wrong voltage, it would still check like a diode. but if the zener is bad, the voltage on C603 should still be around 20v in standby
            Last edited by R_J; 08-23-2020, 07:34 PM.

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              #26
              Re: Sharp LC-50UB30U. Completely dead, no power indicator.

              Originally posted by R_J View Post
              Well it's the standby transformer that supplies that voltage, R606a,b are just low ohm resistors (acting like fuses) D603 is the rectifier diode for the voltage and C603 is the filter. What is the voltage across C603 in standby? It could be that ZD604 is bad and zenering at the wrong voltage, it would still check like a diode. but if the zener is bad, the voltage on C603 should still be around 20v in standby
              C603 in standby: +14.88v, steady.

              Comment


                #27
                Re: Sharp LC-50UB30U. Completely dead, no power indicator.

                Originally posted by HAHOMETP View Post
                C603 in standby: +14.88v, steady.
                When you force the power supply ON does it then come up to around 20v?

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                  #28
                  Re: Sharp LC-50UB30U. Completely dead, no power indicator.

                  Originally posted by R_J View Post
                  When you force the power supply ON does it then come up to around 20v?
                  Just tested. Conditions:
                  CN102-PIN12,13,14 @ zero.
                  CN102, CN103, CN105 disconnected.

                  C603 in standby: +14.7v
                  C603 when CN102-PIN11 pulled up to +5v: +11.7v

                  Comment


                    #29
                    Re: Sharp LC-50UB30U. Completely dead, no power indicator.

                    Received a replacement board today. The seller has 17k+ feedbacks, 99.3% positive. The pic shows a powered up TV with a lit up broken screen and the power indicator on. I have no reason to suspect dishonesty.

                    I installed the board onto the chassis and connected _only_ the mains power cord.

                    C120a and C120b:
                    STANDBY: +162v
                    REMOTE ON: jumps to +364v, then drops down to +223v in 16 seconds, then jumps to +375v and so on.
                    The +12v pin acted the same way also (+10v => +7v => +10v etc).

                    This new PSU acts exactly the same way as my original PSU give or take a few volts.

                    What if the PSU expects something other than +5v delivered via a 1k ballast resistor, like for example a series of pulses or something? What if the PSU is fine and it's the MB that is bad after all?
                    Last edited by HAHOMETP; 08-27-2020, 06:51 PM.

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                      #30
                      Re: Sharp LC-50UB30U. Completely dead, no power indicator.

                      The "pullup" resistor is used to turn on a transistor which turns on an optocoupler, thats about it. It does not require any pulses etc. It could be that the power supply needs to see a working backlight, so if the backlight does not light, the power supply shuts down, without an exact schematic, (or the board in my hands) it is hard to actually tell. If the original and the replacement power supplies are doing the same thing the fault must be elseware.
                      It could also be that this power supply need to see a 1K pullup resistor between +5vsb and Backlight ON/OFF and maybe also Dimming1
                      Check the LED supply voltage between ground and D400 (anode). This should be the unboosted voltage maybe around 100vdc? The cathode of D400 should be the boosted voltage which should be higher (guessing by shopjimmy led set) the boosted voltage should be around 190vdc, if this voltage is over 200vdc as an example I would suspect the led string is open and the PS is shutting down.
                      Last edited by R_J; 08-27-2020, 10:55 PM.

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                        #31
                        Re: Sharp LC-50UB30U. Completely dead, no power indicator.

                        Thanks for the advice, R_J, will check the LEDs. I have a dedicated digital LED tester (a self adjusting current source), will try lighting the LED strips individually. Should be easy since there are only two sets of two wires at CN105. If one pair of wires shows less driving voltage than the other pair it would indicate a burnt LED in that particular strip.

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                          #32
                          Re: Sharp LC-50UB30U. Completely dead, no power indicator.

                          Connected the 230v DC LED tester across the top LED strip at CN105. The strip lit up (visible through a hole in the chassis), the driving voltage settled @ +77.6v.
                          Connected the 230v DC LED tester across the bottom LED strip at CN105. The strip lit up (visible through a hole in the chassis), the driving voltage settled @ +77.7v.

                          It appears that the numbers of lit up individual LEDs in both strips are the same, else I would expect some difference in voltages roughly in the increments between 2.5v and 3v.

                          Will be pulling the LCD screen off to take a look at how the actual LED strips light up.

                          Comment


                            #33
                            Re: Sharp LC-50UB30U. Completely dead, no power indicator.

                            Originally posted by HAHOMETP View Post
                            Will be pulling the LCD screen off to take a look at how the actual LED strips light up.
                            Before taking the TV completely apart decided to connect the MB to the PSU and run the same tests again.

                            CN102, 103 and 105 are connected at the PSU.

                            J1 (System Power) and J2 (Power In) are connected at the MB for the first time for these tests.

                            REMOTE_ON, BACKLIGHT_ON, DIMMER1 and DIMMER2 are all pulled up to +5v via 1k resistors.

                            C120a and C120b:
                            STANDBY: +158v, steady.
                            REMOTE ON: +384v, steady.

                            CN102-PIN9, 10: +12v, steady.
                            CN103-PIN1, 2, 3: +12v, steady.

                            CN105-PIN1 (LED1): +20v, steady.
                            CN105-PIN3 (Vout1): +83v, steady.
                            CN105-PIN5 (LED2): +20v, steady.
                            CN105-PIN7 (Vout2): +83v, steady.

                            The backlight is _not_ lit. No flickering like before, completely dark.

                            If I disconnect the J2 (Power In) from the MB while the J1 (System Power) is still connected - nothing happens.
                            If I disconnect the J1 (System Power) from the MB while the J2 (Power In) is still connected - the voltages start to jump in the sawtooth manner and the backlight starts to flicker as was described earlier.

                            IMO the MB is the prime suspect now. What do you think?
                            Last edited by HAHOMETP; 08-29-2020, 08:49 AM.

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                              #34
                              Re: Sharp LC-50UB30U. Completely dead, no power indicator.

                              Do not use pullup resistors to force the ps on with the main board connected, you will likely damage the main board.
                              You need to monitor the Vout voltage while turning on the tv, I suspect it will jump to over 150v and then drop down to 83v due to over voltage shutdown

                              Comment


                                #35
                                Re: Sharp LC-50UB30U. Completely dead, no power indicator.

                                Originally posted by R_J View Post
                                ...I would suspect the led string is open and the PS is shutting down.
                                Right on the money, R_J!

                                I have a few LED strips pulled over time from various TVs with broken screens (mostly VIZIOs) - should be able to find replacement LED chips. I don't think some variance in the colour temperature if any will be visible through the diffusers.

                                Attached are the two pairs of pix: (the LED channel + its driving voltage as indicated by the LED tester) x 2.
                                Attached Files
                                Last edited by HAHOMETP; 09-10-2020, 05:57 PM.

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                                  #36
                                  Re: Sharp LC-50UB30U. Completely dead, no power indicator.

                                  I don't repair LED strips if I can find new strips for a reasonable price. All the LEDs have wear and are likely to fail even with the backlight turned down.

                                  Comment


                                    #37
                                    Re: Sharp LC-50UB30U. Completely dead, no power indicator.

                                    You are right, neilc6. A quick search on Sharp LC-50UB30U reveals four threads (this one included), all of which site burnt LEDs as the cause of malfunction. Apparently Sharp used some garbage LEDs in this particular model/family.

                                    Still, just for giggles with a heat gun and solder paste in hand I replaced two individual LEDs (circled in GRN) on one strip, combined 4 good strips into one good channel and powered it up. The channel lit up and within a couple of minutes yet another LED went dim (circled in RED). Repairing these subpar strips makes no economic sense.

                                    I have a bunch of various LED strips scavenged off broken TV sets over the years, none of which is a perfect match. There is one set of strips with the perfect 63mm spacing between the LEDs but alas, the LEDs are of the 5.2v variety. I also have the proper 2.6v LED strips but none of them are even close to the required pitch. Plus some of them are arranged in 2x3, 3x4, 4x2, 7x1 and other configurations so some rewiring will be needed as well. Back to the drawing board so to speak...

                                    I've put together an LED schematic just in case for future reference. Plz disregard the connector p/nos: I pulled those randomly from the built-in Eagle library.
                                    Attached Files
                                    Last edited by HAHOMETP; 09-16-2020, 06:57 PM.

                                    Comment


                                      #38
                                      Re: Sharp LC-50UB30U. Completely dead, no power indicator.

                                      Hello, folks.

                                      Had to sidetrack the project a bit. Anyway...

                                      Replaced all of the OE LED strips with those from a Vizio. Will post pix if there is interest. What I did not take into the account was the lower working current of the Vizio LEDs.

                                      CURRENT (ma) as MEASURED for 1 LED @ 3.3v
                                      SHARP 460
                                      VIZIO 240

                                      The LEDs light up and shut down just as it has been described in post #3 of this thread.

                                      Each pair of LED strips is driven by one BD9489F. Is there a way to tell this chip to accept a lower working current by changing some resistors? I am attaching detailed pictures of the LED driver circuits.

                                      LED driver channel x 2.

                                      IC300, IC400 (LED driver): BD9489F
                                      Q300, Q400 (N-Channel Enhancement Mode MOSFET): P0920AD
                                      Q301, Q401 (N-channel MOSFET 200V): MDD7N20C
                                      Attached Files
                                      Last edited by HAHOMETP; 12-04-2020, 03:30 PM.

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