PSU with FAN8754 won't torn on

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  • fejlong
    Senior Member
    • Dec 2013
    • 55
    • United Kingdom

    #1

    PSU with FAN8754 won't torn on

    Hello everyone,
    Recently I got an LED TV Hannspree HSG1210 with no power symphtom.
    The power supply is a 40-P081C0-PWD1XG, I could not find a schematic for it other than from a similar TV, Philco PH32.
    The power board has a VIPER17L which makes 3.3V, and a FAN8754 which is not working or won't start.
    The VIPER17L is working and 3.3V is present. FAN8754 is making a rattling sound and does not operate the power mosfet.
    I have changed the FAN8754 and the power mosfet, thinking they are defective. But the 24V still does not appear.
    The four rectifier diodes I did change, still not working, I have 300V on the HV cap. there is near to 0V all the time on the power mosfet's gate. so the fan is not control it.
    Anyone knows where can I continue troubleshooting ?
    Any info whould be much apreciated
    Attached Files
  • ReeceyBurger123
    Never Give Up !
    • May 2014
    • 7325
    • Britain

    #2
    Re: PSU with FAN8754 won't torn on

    First of all you need to make sure the motherboard is telling the Psu to come on, what is the Pson voltage at ?
    Please Do Not PM My Page Asking For Help Badcaps Is The Place For Advise, Page Linked For Business Reasons Only. Anyone Doing So Will Be Banned Instantly !

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    Comment

    • CapLeaker
      Leaking Member
      • Dec 2014
      • 7992
      • Canada

      #3
      Re: PSU with FAN8754 won't torn on

      no boosted voltage on the primary filter cap(s) = no 24V.
      Last edited by CapLeaker; 09-25-2016, 04:50 PM.

      Comment

      • fejlong
        Senior Member
        • Dec 2013
        • 55
        • United Kingdom

        #4
        Re: PSU with FAN8754 won't torn on

        Pson it is labeled P-ON, and it is about 3.2V

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #5
          Re: PSU with FAN8754 won't torn on

          Did you find the spec sheet for the 'FAN8754'? Need to find out if you have VCC to run the IC or not, I expect around 15 VDC.
          R112 is less than 1 Ohm?
          Last edited by budm; 09-25-2016, 10:23 PM.
          Never stop learning
          Basic LCD TV and Monitor troubleshooting guides.
          http://www.badcaps.net/forum/showthr...956#post305956

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          http://www.badcaps.net/forum/showthr...999#post300999

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          http://www.badcaps.net/forum/showthr...er+testing+cfl

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          Comment

          • fejlong
            Senior Member
            • Dec 2013
            • 55
            • United Kingdom

            #6
            Re: PSU with FAN8754 won't torn on

            Sorry for that, It's a FAN6754. I am attaching the datasheet.

            Resistor R112 is labeld as 0.15 Ohm, with the multimeter it shows 0.2 Ohm.

            Supply Pin 7 of IC has 18.5V ,

            HV pin 4 should be at least 104V according to the datasheet page 5 high voltage section, and this has only 94.5V don't know what is causing this
            Attached Files

            Comment

            • dick_barton
              Badcaps Legend
              • Aug 2015
              • 6642
              • Wales

              #7
              Re: PSU with FAN8754 won't torn on

              Check the components connected to it. D101, R102 (563 = 56K), Rxxx (104 = 100K) in series with it.

              Edit
              18.5V for pin 7 (VCC) is above the spec for the chip to operate. Vcc min is stated as 15.5V, typical 16,5V, maximum 17.5V

              What's the voltage on the feedback pin 2 which should be <4.6V
              Last edited by dick_barton; 09-26-2016, 04:00 AM.
              Willing to help but I'm no expert.

              Comment

              • dick_barton
                Badcaps Legend
                • Aug 2015
                • 6642
                • Wales

                #8
                Re: PSU with FAN8754 won't torn on

                The mosfet pin needs to be soldered and looking at your photo there appears to be a solder shard between pins 1 & 2 of the FAN chip although it could just be the lighting.
                Attached Files
                Willing to help but I'm no expert.

                Comment

                • fejlong
                  Senior Member
                  • Dec 2013
                  • 55
                  • United Kingdom

                  #9
                  Re: PSU with FAN8754 won't torn on

                  I have did a check on those components, everything looks good.

                  initalIy I have changed the mosfet, the solder is good on the mosfet, may it stil has some flux on that area.

                  Comment

                  • dick_barton
                    Badcaps Legend
                    • Aug 2015
                    • 6642
                    • Wales

                    #10
                    Re: PSU with FAN8754 won't torn on

                    Originally posted by dick_barton
                    What's the voltage on the feedback pin 2 which should be <4.6V
                    And is that a small slither of solder between pins 1 & 2 of the IC or just a reflection of the light on the photo?
                    Willing to help but I'm no expert.

                    Comment

                    • fejlong
                      Senior Member
                      • Dec 2013
                      • 55
                      • United Kingdom

                      #11
                      Re: PSU with FAN8754 won't torn on

                      Between pins 1 and 2, It is flux wich remained after replacing the IC.

                      I will check the voltage on the feedback pin and be back to you.

                      Attached some close up pics of the IC
                      Attached Files
                      Last edited by fejlong; 09-26-2016, 05:57 AM.

                      Comment

                      • fejlong
                        Senior Member
                        • Dec 2013
                        • 55
                        • United Kingdom

                        #12
                        Re: PSU with FAN8754 won't torn on

                        On feedback pin 2 is 2V

                        Comment

                        • fejlong
                          Senior Member
                          • Dec 2013
                          • 55
                          • United Kingdom

                          #13
                          Re: PSU with FAN8754 won't torn on

                          There is only 2V on the feedback pin, what does this means?
                          Where should I look for the problem?

                          Comment

                          • dick_barton
                            Badcaps Legend
                            • Aug 2015
                            • 6642
                            • Wales

                            #14
                            Re: PSU with FAN8754 won't torn on

                            The datasheet says that if FB > 4.6V for more than 55mS then it latches off the PWM.
                            With 2V at this pin then that is not the problem.
                            Willing to help but I'm no expert.

                            Comment

                            • dick_barton
                              Badcaps Legend
                              • Aug 2015
                              • 6642
                              • Wales

                              #15
                              Re: PSU with FAN8754 won't torn on

                              Originally posted by fejlong
                              initalIy I have changed the mosfet
                              Was that with an identical part or substitute?
                              Willing to help but I'm no expert.

                              Comment

                              • dick_barton
                                Badcaps Legend
                                • Aug 2015
                                • 6642
                                • Wales

                                #16
                                Re: PSU with FAN8754 won't torn on

                                You are correct regarding the HV pin input voltage being low. I would be tempted to replace the two resistors and diode feeding it and see if the voltage at the HV pin increases.
                                Willing to help but I'm no expert.

                                Comment

                                • fejlong
                                  Senior Member
                                  • Dec 2013
                                  • 55
                                  • United Kingdom

                                  #17
                                  Re: PSU with FAN8754 won't torn on

                                  I tried that, no change

                                  Comment

                                  • dick_barton
                                    Badcaps Legend
                                    • Aug 2015
                                    • 6642
                                    • Wales

                                    #18
                                    Re: PSU with FAN8754 won't torn on

                                    What is the voltage at the other end of the diode and resistors?
                                    Willing to help but I'm no expert.

                                    Comment

                                    • fejlong
                                      Senior Member
                                      • Dec 2013
                                      • 55
                                      • United Kingdom

                                      #19
                                      Re: PSU with FAN8754 won't torn on

                                      Regarding wich ground ?

                                      Comment

                                      • dick_barton
                                        Badcaps Legend
                                        • Aug 2015
                                        • 6642
                                        • Wales

                                        #20
                                        Re: PSU with FAN8754 won't torn on

                                        The same ground as you used to measure the 17.5V in post #6

                                        Edit
                                        What is your mains supply voltage to the set.
                                        Last edited by dick_barton; 09-27-2016, 04:43 AM.
                                        Willing to help but I'm no expert.

                                        Comment

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