LG32 no 24v line

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • yogurt
    New Member
    • Aug 2011
    • 8

    #1

    LG32 no 24v line

    Hello all,

    My problems is like this:

    LG32 LG5000 turns on but picture is black. Backlight is not working. I found 4 A4614 transistors shorted and have taken them out. Still 4 left. I used an external power supply to check if the lamps are ok and yes, they all work. Because there is nowhere i can find A4614, a friend told me that IRF7389 will work the same. Oh boy was he wrong.... I soldered 4 new transistors and TV turned on for couple of seconds and BANG. A fuse blows. I test why the fuse blew, and I find 2 shorted mosfets. OK, so I replace the mosfets and the fuse, TV turns on but there is no 24v anymore only 1.2v. I disconnected the inverter board thinking maybe something was drawing power and triggering overload protection. Still no 24v. Then I start looking around to see if any resistors might have gone with the mosfets and the fuse but no luck. Everything tests out fine. What else could be damaged when the mosfets have blown to take out 24v line?
  • yogurt
    New Member
    • Aug 2011
    • 8

    #2
    Re: LG32 no 24v line

    Pictures
    Attached Files

    Comment

    • PlainBill
      Badcaps Legend
      • Feb 2009
      • 7034
      • USA

      #3
      Re: LG32 no 24v line

      The pictures help a little.

      The 'A4614' are probably AO4614; they are available from a number of sellers on eBay - 10 will cost about $11 delivered.

      On the power supply, check the diodes (they look like power transistors) on the heat sink closest to the connector for the inverter.

      Compare the original A4614 to the Alpha and Omega datasheet, paying particular attention to the logo to confirm that is the correct part.

      If you have difficulties with the diodes, a picture of the bottom side of the power supply will help troubleshoot.

      PlainBill
      For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

      Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

      Comment

      • yogurt
        New Member
        • Aug 2011
        • 8

        #4
        Re: LG32 no 24v line

        Thank you for the quick reply,

        I checked the diodes out of circuit MBRF10100CT and they test OK.

        Yes it is indeed the AO4614, sorry for the typo. We can't order from ebay in my country so I am forced to find something locally or find some distant relative that I can pay to mail me the parts.

        I forgot to take the bottom picture, i will upload the photo tomorrow when my camera is available to me. Any other things i could test in the mean time?

        Comment

        • PlainBill
          Badcaps Legend
          • Feb 2009
          • 7034
          • USA

          #5
          Re: LG32 no 24v line

          Originally posted by yogurt
          Thank you for the quick reply,

          I checked the diodes out of circuit MBRF10100CT and they test OK.

          Yes it is indeed the AO4614, sorry for the typo. We can't order from ebay in my country so I am forced to find something locally or find some distant relative that I can pay to mail me the parts.

          I forgot to take the bottom picture, i will upload the photo tomorrow when my camera is available to me. Any other things i could test in the mean time?
          The 1.2 volts is instructive. Was that with the inverter connected or disconnected? 1.2Volts suggests the SMPS controller is working, but is current limiting. Eitehr something (the inverter) is overloading it, there is a damaged current sense resistor, or there is a drive problem.

          PlainBill
          For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

          Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

          Comment

          • yogurt
            New Member
            • Aug 2011
            • 8

            #6
            Re: LG32 no 24v line

            Before the mosfet accident, I had 24v with and without inverter board. Now it is 1.2v with and without inverter hooked up. I took out all fuses on the inverter to stop the mosfets from blowing up.

            Good news is I found a way to order stuff from ebay so those ao4614 are coming

            If now only we could get it to fire up 24v the tv would be fixed.

            One thing i noticed and it might be helpful info to you> Mosfets are now giving out erratic voltages-from 0-150V DC. Maybe it is something before the large transformer underneath the inverter connector that is the culprit?

            Pictures are coming within the hour too. Found a camera

            Comment

            • yogurt
              New Member
              • Aug 2011
              • 8

              #7
              Re: LG32 no 24v line

              More pictures
              Attached Files

              Comment

              • PlainBill
                Badcaps Legend
                • Feb 2009
                • 7034
                • USA

                #8
                Re: LG32 no 24v line

                Probably not the mosfet. If it were bad you wouldn't get anything. Most SMPS designs have a low value (< 10 ohm) resistor between the source pin of the MOSFET and Ground. The SMPS controller monitors the voltage across that resistor and will reduce the drive to the FET if the voltage gets too high. That resistor may be damaged, or the SMPS controller may be damaged.

                PlainBill
                For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                Comment

                • yogurt
                  New Member
                  • Aug 2011
                  • 8

                  #9
                  Re: LG32 no 24v line

                  I was not able to find a bad smd resistor between replaced mosfets source and ground. They all checkout. But, I have found two probably bad resistors marked A and B in the picture:

                  A: colors: Blue, Violet, Black, Gold = 5,5 Ohm Should be 68 Ohm
                  B: colors: Red, Red, Gold, Gold = 0.03 Ohm Should be 2,2 Ohm

                  I will replace them later today. Can they be the source of my problems, or have I discovered something even more wrong with this board?
                  Attached Files

                  Comment

                  • PlainBill
                    Badcaps Legend
                    • Feb 2009
                    • 7034
                    • USA

                    #10
                    Re: LG32 no 24v line

                    Originally posted by yogurt
                    I was not able to find a bad smd resistor between replaced mosfets source and ground. They all checkout. But, I have found two probably bad resistors marked A and B in the picture:

                    A: colors: Blue, Violet, Black, Gold = 5,5 Ohm Should be 68 Ohm
                    B: colors: Red, Red, Gold, Gold = 0.03 Ohm Should be 2,2 Ohm

                    I will replace them later today. Can they be the source of my problems, or have I discovered something even more wrong with this board?
                    The possible bad resistor would not be an SMD resistor; the two you identified would be potential suspects, but it is unlikely they are the cause for several reasons.
                    1. I would expect them to be a lower resistance. I just checked the power supply schematic for a similar TV; they used .12 ohm resistors.

                    2. The resistor would fail high

                    3. I would expect the resistors to be in the area of Q110.

                    4. R123 (hidden under a dab of glue) is a possible suspect. THAT IS A GUESS; I have not had my eyes open wide enough to do a decent examination of the pictures.

                    PlainBill
                    For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                    Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                    Comment

                    • yogurt
                      New Member
                      • Aug 2011
                      • 8

                      #11
                      Re: LG32 no 24v line

                      No luck, replaced those resistors and the same problem exists. I checked and there are no other resistors near Q110 except that R123. It has 120K ohms on the meter and its colors say that aswell.

                      Do you have any other ideas what i could check? How can we test that SMPS controller?

                      I checked all other mosfets for shorts and they are all ok. All diodes checked and ok. What can I do to give you more info, so we can trace the problem?

                      Comment

                      • PlainBill
                        Badcaps Legend
                        • Feb 2009
                        • 7034
                        • USA

                        #12
                        Re: LG32 no 24v line

                        Since you ask, I need a decent picture of the bottom of the power supply. The pictures you provided of the top were quite good; those of the bottom were inadequate.

                        I need something well lit, and sharply focused. The recommendation is to put the camera in macro mode and turn off the flash. The limits on this site are 2000 x 2000 pixels; get as close to that as possible. Before you upload one, take a look at it. If you can't read component IDs, it doesn't really help me.

                        PlainBill
                        For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                        Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                        Comment

                        Related Topics

                        Collapse

                        • BlackScreen_22
                          Harman Kardon sub TS11 (ds15 amplifer) blows fuse and mosfets
                          by BlackScreen_22
                          Hi, I'll start by saying that I'm not an expert and I've reached a point where I don't know what to try/do anymore...
                          Starting from the beginning: I opened this subwoofer for the first time with a very strong smell of burnt electrical components, I realize that on the amplifier board there is a hole between V+ OUT and GND about the size of a finger, the damaged components were the shorted mosfets, two damaged zener diodes and two capacitors. I bought everything, I fixed the hole by cutting the pcb and putting a piece of a perforated board.
                          I had no problems connecting mosfets and capacitors,...
                          08-27-2024, 12:46 PM
                        • NanoTesting
                          Lenovo Ideapad 15IIL05, turns on and off with charger BUT works by injecting 20v after main mosfets
                          by NanoTesting
                          I got a 15-IIL05 that failed to turn on BUT IT DID TRY TO TURN ON and then turned off after 30+- seconds, i disassembled it and found a screw loose inside the case.
                          With charger it turns on, fan spins but gives no image.
                          Tested main mosfets no short, tested 3.3v,5v,DRAM, CPU etc and they were present.
                          Reflashed BIOS, same problem.
                          Replaced both main mosfets.
                          Checked main mosfets again and i noticed that they closed once the laptop shut down, so i decided to bypass them and used a bench PSU to check how much power the laptop was drawing while trying to turn on, 20v@3A,...
                          10-30-2024, 10:48 PM
                        • corrize
                          A funny fuse story – Lumix LX100 II
                          by corrize
                          Hello, I disassembled this dead camera, and found this WTF… Two fuses soldered one above the other !
                          I was pretty sure nobody touched it before, but that can't be from factory. There is flux, and capacitor is probably missing.
                          The other weird thing : the fuses are « G » fuse : (0.75A – 8V), seems very low. The original fuse should be « O » : (32V 2,5A).
                          There is « O » mark beside. All fuses have the same mark letter on main board. So, I can deduce it's a « O » fuse.
                          And this correspond to the issus I saw : when I plug the battery, I measure the voltage dropping...
                          10-19-2023, 09:58 AM
                        • cheeky2
                          Samsung BN44-00262A H37F1-9SS power supply help finding blown value components!
                          by cheeky2
                          This Samsung combined power supply and inverter was replaced a while ago from a Samsung 37inch LE37B530P7W TV. However I would like to repair this one.
                          I have replaced the Mosfets Q1820 and Q1821 ( FDPF7N50U) which were both blown and the fuse FM802S. The schematic for this power supply that is attached doesn't relate to this power supply as the driving transistors and diodes are D1830, D1831, D1832, D1833, Q1811 & Q1810 are nowhere on the schematic!
                          Does anyone know what the components for D1830, D1831, D1832, D1833, Q1811 & Q1810 should be? I ask as I did change the Mosfets...
                          06-15-2025, 05:12 AM
                        • AccountSaver
                          Lenovo Thinkpad E15 Gen 2 NM-D011 - No display ? External , yes!
                          by AccountSaver
                          Here is a pretty crazy one.

                          Step 1.
                          Laptop was brought to me as dead not working. Removed everything , cleared everything.
                          Step 2.

                          Some liquid damage close to the Type - C connector, and the connector even though it was cleaned wasn't charging the battery . Removed the Type-C port, and replaced it. Now the laptop turns on and charges battery. Shows external screen , not internal.
                          Step 3.

                          Took out the screen and checked it to a secondary Gen 2 i have, screen works like a charm.
                          Step 4.

                          Lets ,dive into the board. I see the edp cable on the...
                          05-07-2025, 07:16 AM
                        • Loading...
                        • No more items.
                        Working...