LG 42LB5600 TV with faulty EAX65423701 PSU

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  • Dannyx
    CertifiedAxhole
    • Aug 2016
    • 3912
    • Romania

    #1

    LG 42LB5600 TV with faulty EAX65423701 PSU

    Good day folks. Let's get straight to the point: I've got what I think is a pretty recent model of LG LED TV which has a power supply issue. The TV is a 42LB5600. I've searched around and I found posts about other models pretty similar to this, but not the exact problem (though I kinda know what to look for), so I'll leave my own thread here so that I can hopefully get some more tips from those more professional than I am (haven't quite worked with LGs that much).

    The problem: the TV does not turn on and the power LED on the front is flickering (not flashing steadily as if TRYING to come on).

    My thoughts based on what I read so far: bad PFC.

    My observations so far (bare with me, as I haven't quite measured everything I should've, but I'll open the thread in advance anyway): the power supply is an EAX65423701. Plug the TV in and the power supply starts making a rapid ticking noise (4-5 clicks per second, in time with the LED flickering). The 3.5V stand-by is present at the connector for the main board. Applying 3 volts to the main board with a computer power supply keeps the LED lit steadily, so I highly doubt the main board is at fault. Disconnecting the main board from the power supply does NOT turn on the backlight - the ticking noise continues and no voltage comes out of the LED plug at the top ! The voltage at the main cap jumps between 317V and 322V in between each of those clicks, indicating that it tries to fie on but fails, as it should go up to around 380v and stay there, so I'm suspecting a PFC issue, though I haven't yet ruled out the possibility of something bad in the secondary causing the immediate shutdown. All the diodes that I checked are good. Fuses are good. Caps show no sign of wear (though I don't have an ESR meter on hand yet - will get one soon). Another thing I checked were those 4 SMD diodes on the back encircled in red in the third pic (7503 = 750 Kohms - can't see them too well due to the glare) and I find their values to be a bit low, only around 500 Kohms on all of them, which is strange, since resistors usually increase their resistance when they fail and not the other way around ! :|

    What I haven't tried yet: reflowing connections to transistors/transformer etc, heating up the board while on, checking the power to those 2 ICs on the HOT side (which is going to be a pain, since they're covered in some sort of raisin and I can't even friggin' see what they are, let alone measure them ! ).
    That's about it for now...thanks in advance for all the help. Cheers.
    Attached Files
    Wattevah...
  • dick_barton
    Badcaps Legend
    • Aug 2015
    • 6642
    • Wales

    #2
    Re: LG 42LB5600 TV with faulty EAX65423701 PSU

    If the PFC is trying to run then maybe as you say there's a problem on the secondary side. I found that measuring the resistances (7503) in circuit was hopeless and would measure perfectly when lifted out of circuit.
    What PFC chip does it use.
    Last edited by dick_barton; 09-03-2016, 02:59 PM.
    Willing to help but I'm no expert.

    Comment

    • Dannyx
      CertifiedAxhole
      • Aug 2016
      • 3912
      • Romania

      #3
      Re: LG 42LB5600 TV with faulty EAX65423701 PSU

      Originally posted by dick_barton
      If the PFC is trying to run then maybe as you say there's a problem on the secondary side. I found that measuring the resistances (7503) in circuit was hopeless and would measure perfectly when lifted out of circuit.
      What PFC chip does it use.
      I too started thinking about a short in the secondary (yesterday night when I was on the toilet LOL - that's where the best ideas come). I can't remember for sure what the PFC IC is (the one towards the bottom right I assume), as I don't have the board on hand right now - it's at work and I'm at home. I'll check, search for the datasheet and measure the VCC pin, right ? If that's good, then perhaps the PFC is indeed working ? I'll then move my search in the secondary side, though on quick inspection all diodes seemed OK (no beeps on the meter's continuity setting). I know there's a whole lot of other components that can become shorted, but I haven't checked them yet - will do that tomorrow.
      Wattevah...

      Comment

      • CapLeaker
        Leaking Member
        • Dec 2014
        • 8135
        • Canada

        #4
        Re: LG 42LB5600 TV with faulty EAX65423701 PSU

        check the transistor and the 4 diodes on that large heat sink on the secondary make sure there is nothing shorted there first.
        Last edited by CapLeaker; 09-04-2016, 06:48 AM.

        Comment

        • Dannyx
          CertifiedAxhole
          • Aug 2016
          • 3912
          • Romania

          #5
          Re: LG 42LB5600 TV with faulty EAX65423701 PSU

          Originally posted by CapLeaker
          check the transistor and the 4 diodes on that large heat sink on the secondary make sure there is nothing shorted there first.
          I already did - they all seem fine (at least on quick check with the continuity setting, as it produced no "beeps"). I'll then check the LED driver IC, see if it's shorted.
          Wattevah...

          Comment

          • Dannyx
            CertifiedAxhole
            • Aug 2016
            • 3912
            • Romania

            #6
            Re: LG 42LB5600 TV with faulty EAX65423701 PSU

            Originally posted by dick_barton
            If the PFC is trying to run then maybe as you say there's a problem on the secondary side. I found that measuring the resistances (7503) in circuit was hopeless and would measure perfectly when lifted out of circuit.
            What PFC chip does it use.
            The PFC IC is a MAP8800 - just checked it
            Wattevah...

            Comment

            • Dannyx
              CertifiedAxhole
              • Aug 2016
              • 3912
              • Romania

              #7
              Re: LG 42LB5600 TV with faulty EAX65423701 PSU

              I made another discovery: the resistor in the picture ! It goes between the drain and source of the 2 D-PAK FETs on the left side of the board (on the back) and ground (also discharging the 2 blue caps that are there apparently). My question: what value do you guys think this is supposed to have as I don't have a schematic and don't know which direction I should read the bands: 53.5 mega Ohms (reading the bands from left to right: green, yellow, green green, brown), or 155 Kohms (reading the bands from right to left: brown, green, green, yellow, green). Either way, I measured it with my meter (out of circuit) and the resistance I get is 1,5 Meg. Ohms, which is off in both ways. I know resistors usually tend to increase their resistance when they fail, so that's why I'm leaning towards it being a 150k Ohm which went bad and jumped to 1 Meg....just a thought. Cheers.
              Attached Files
              Wattevah...

              Comment

              • CapLeaker
                Leaking Member
                • Dec 2014
                • 8135
                • Canada

                #8
                Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                brown, green, green, yellow, green= 1,55 MOhm.

                nuttn wrong with that resistor.

                Comment

                • Dannyx
                  CertifiedAxhole
                  • Aug 2016
                  • 3912
                  • Romania

                  #9
                  Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                  Originally posted by CapLeaker
                  brown, green, green, yellow, green= 1,55 MOhm.

                  nuttn wrong with that resistor.
                  Call me a noob, but how did u figure it out ? You have a schematic or something ? I quickly realized it's not that, since I plugged in the PSU without it (I left one leg pulled out just like in the pic) and nothing changed - same ticking sound and no output. Actually, the output cap C224 DOES shoot up to 130 volts for a brief moment after plugging the board in, then it slowly drains, indicating that it receives a bit of power which is then cut off for some reason. Still couldn't find any shorts (not even in the ICs themselves), so I'm pretty stuck right now. I tried heating up the board, especially the optocoupler area, but it didn't change jack-sh!t. Not having an ESR meter yet, I'll try changing the large blue cap near the transformer, since that's where the ticking come from - I know a cap can't actually make any sound and it's the transformer that makes it, but it pointed me in that general area. The MAP8800 PFC IC is receiving power on the VCC pin (can't remember how much, I think 122V, but I think we can conclude the PFC side is working, since the main cap stays at 320V and tries to go higher but can't).
                  Wattevah...

                  Comment

                  • vinceroger69
                    Badcaps Legend
                    • Mar 2012
                    • 6714
                    • uk

                    #10
                    Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                    http://resistor.cherryjourney.pt/

                    Comment

                    • Dannyx
                      CertifiedAxhole
                      • Aug 2016
                      • 3912
                      • Romania

                      #11
                      Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                      Originally posted by vinceroger69
                      I'm familiar with the colour coding of resistors. Sorry, I wasn't specific enough, my question was how CapLeaker figured out the ORDER of the bands (not what numbers they signify). The bands on each end are placed in exactly the same spot, so how do I know if read them from the left or from the right ? The green band at the end can signify both a value and a tolerance percentage.
                      Wattevah...

                      Comment

                      • Dannyx
                        CertifiedAxhole
                        • Aug 2016
                        • 3912
                        • Romania

                        #12
                        Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                        Also, I can't find any data on that 16 pin SMPS IC. After I peeled away that raisin it was covered in, I can read 6N14549 and 6A01 under that, but neither of these returned any useful searches...actually, I did find something: its full name is apparently FA6A01, but the only datasheet I could find was no longer available (page not found). I then found something similar to it, which is this guy here, but it's an FA6A00N....not exactly the same thing and I doubt the pinout is the same: pin 10 is VCC in the datasheet, but pin 10 on my IC is the gate driver for one of the FETs....darn ! )
                        Wattevah...

                        Comment

                        • dick_barton
                          Badcaps Legend
                          • Aug 2015
                          • 6642
                          • Wales

                          #13
                          Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                          Originally posted by Dannyx
                          I'm familiar with the colour coding of resistors. Sorry, I wasn't specific enough, my question was how CapLeaker figured out the ORDER of the bands (not what numbers they signify). The bands on each end are placed in exactly the same spot, so how do I know if read them from the left or from the right ? The green band at the end can signify both a value and a tolerance percentage.
                          Reading it one way compares favourably to what it measures so I guess that is the way you read it. If it did not compare then it would have posed a problem.
                          Willing to help but I'm no expert.

                          Comment

                          • dick_barton
                            Badcaps Legend
                            • Aug 2015
                            • 6642
                            • Wales

                            #14
                            Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                            Your PFC is a MAP8800 which a Russian website says can be replaced by a FAN6961 with one resistor modification. The minimum VCC required for the FAN6961 to run is typically 12.5V. What is the dc voltage between pin 8 (VCC) and pin 6 (GND) of your MAP8800?
                            Willing to help but I'm no expert.

                            Comment

                            • Dannyx
                              CertifiedAxhole
                              • Aug 2016
                              • 3912
                              • Romania

                              #15
                              Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                              Originally posted by dick_barton
                              Your PFC is a MAP8800 which a Russian website says can be replaced by a FAN6961 with one resistor modification. The minimum VCC required for the FAN6961 to run is typically 12.5V. What is the dc voltage between pin 8 (VCC) and pin 6 (GND) of your MAP8800?
                              The pinout of the MAP doesn't seem to match the one of the FAN. Vcc is pin 1 on the MAP (not pin 8) while GND is pin 8. Anyhow, measuring those 2 pins shows 2.1v....oops, I definitely think something's wrong there :| Funny thing is that I DID measure those pins earlier today and I thought I saw 21V on my meter, but it was actually 2.1 LOL ) What could cause this lack of power ? I'm guessing some of those SMD components around the MAP...I shall upload a close-up.
                              Wattevah...

                              Comment

                              • Dannyx
                                CertifiedAxhole
                                • Aug 2016
                                • 3912
                                • Romania

                                #16
                                Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                                Ok, my bad. I thought I found the pinout here, but taking a closer look at the board reveals that it's not correct (the pins are arbitrarily laid out in that diagram), so Pin 8 seems to be Vcc, while pin 6 is GND, so Dick was definitely right ...I should've seen it from a mile away and testing with a multimeter showed just that: a solid "beep" between pin 6 and GND...sorry, will measure again I attached a close-up of the MAP8800.
                                Attached Files
                                Wattevah...

                                Comment

                                • dick_barton
                                  Badcaps Legend
                                  • Aug 2015
                                  • 6642
                                  • Wales

                                  #17
                                  Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                                  On your image above some of the solder joints on the IC pads look as though they are bridged across to the next pad with solder whiskers.

                                  Here are some images of the IC's FAN6961 & MAP8800
                                  Attached Files
                                  Last edited by dick_barton; 09-05-2016, 11:06 AM.
                                  Willing to help but I'm no expert.

                                  Comment

                                  • Dannyx
                                    CertifiedAxhole
                                    • Aug 2016
                                    • 3912
                                    • Romania

                                    #18
                                    Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                                    Okay, now I feel like an idiot: I totally forgot to short the PS ON pin to 3.5 v during all my tests so far, so I did that now and.....wtf ? Power supply turned on :| 12v, 24v, hell even 86v on the led output, everything was there :| Before you start calling me a total loser (which I am at this point), check this out: earlier on today I DID replace 2 capacitors on the control side of the primary, one of which is directly connected to the VCC pin of the MAP IC, so maybe that indeed got it going, since I haven't tested it since.....either that, or the main board is indeed defective, which would be a tremendous shame after all this trouble I put you guys through I doubt it's the board though, since I applied 3 volts to its standby pin with a computer power supply and the power LED lit steadily, instead of flickering like it did when I connected the apparently faulty power board....what do you guys think ? Have you seen faulty LG boards before ? Thanks for all your help so far - best forum evah brah !
                                    Wattevah...

                                    Comment

                                    • CapLeaker
                                      Leaking Member
                                      • Dec 2014
                                      • 8135
                                      • Canada

                                      #19
                                      Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                                      Ever thought about to measure the current draw of the main board? Maybe it draws more that the VSB rail of the PSU can handle? So put that main board back on the PSU and retest.

                                      Also check the main board VSB rail with your ohm meter between the GND and VSB rail, maybe there is a short? Check the others too on the main board.
                                      Last edited by CapLeaker; 09-05-2016, 01:14 PM.

                                      Comment

                                      • Dannyx
                                        CertifiedAxhole
                                        • Aug 2016
                                        • 3912
                                        • Romania

                                        #20
                                        Re: LG 42LB5600 TV with faulty EAX65423701 PSU

                                        Originally posted by CapLeaker
                                        Ever thought about to measure the current draw of the main board? Maybe it draws more that the VSB rail of the PSU can handle? So put that main board back on the PSU and retest.

                                        Also check the main board VSB rail with your ohm meter between the GND and VSB rail, maybe there is a short? Check the others too on the main board.
                                        I shall tomorrow - I took the board home with me tonight to work on it, so the rest of the TV is at work....fingers crossed
                                        Wattevah...

                                        Comment

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