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AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

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    AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

    I have a AOC 2236Vw, Model TFT22W90PS
    The monitor refuses to power on. When I plug the power cord, the monitor's blue power light turns on, then after about 1 second, I hear a faint "tick", and the power light shuts off.

    I disassembled, and found "Elite" brand caps. None looked out of the ordinary, but I replaced them anyway, with Nichicon VZ series I had laying around. One cap I did NOT replace, was the orange cap labelled C920, an "Elite GP" series which I couldnt find a datasheet for a suitable replacement.
    Replacing caps had no effect.

    I also suspected the CCFL lamps may be bad, so I plugged in a couple of spares out of a Dell monitor.
    Replacing CCFL lamps had no effect

    At this point I'm chasing my tail, I don't know what else to look for. The board is heat-checked around the inverter transformer, but I see no other signs of damage.
    This looks like a very common design power supply, and the logic board looks identical to ones out of many threads I've read.

    Any suggestions to what I should look for next?
    Attached Files
    Last edited by fuxxy; 05-10-2016, 04:27 PM.

    #2
    Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

    AOC 2236Vw Service Manual
    Attached Files
    Last edited by fuxxy; 05-10-2016, 05:49 PM. Reason: Correct revision manual, with updated Power Supply schematic

    Comment


      #3
      Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

      I get a solid 5.17VDC from the 8 pin connector on the power supply, even wen the blue power light is off
      Aside from +5VDC and GND, the other wires are labelled MUTE, VOL, ON/OFF, and DIM. I don't know if those will be useful for testing
      Last edited by fuxxy; 05-10-2016, 04:40 PM.

      Comment


        #4
        Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

        I've been reading another post with a similar issue on a similar design here- https://www.badcaps.net/forum/showthread.php?t=50657

        In that thread, the OP mentions he shocked himself on one of the heatsinks. It looks like a double-schottkey - in my power supply I think the matching heatsink is HS1, with Q901 attached. I made the same measurement as he did from one of the GND pins to the heatsink HS1, and I get -78VDC. I don't know what this means, but it seems similar.

        Comment


          #5
          Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

          Q805 & Q806 Resistance check (Source-to-Drain)

          Q805
          Pin 1 to common drain = short, 0 ohms
          Pin 3 to common drain = short, 0 ohms

          Q806
          Pin 1 to common drain = short, 0 ohms
          Pin 3 to common drain = short, 0 ohms

          I'm inferring from the other thread that these shorts would overload the power supply. Are these components the cause?

          Comment


            #6
            Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

            well, it appears that the shorted mosfets are no longer shorted once I removed them from the circuit.

            Comment


              #7
              Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

              Removed backlight driver FETs Q805 & Q806
              Power supply starts up, steady 5V and steady 16V output. (no backlights, obviously. Image is displayed on screen when lit with flashlight)

              Comment


                #8
                Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                Reinstalled FETs Q805 & Q806.

                Installed a 4.7Kohm resistor between backlight driver IC801 "timer" pin 12 and GND to disable shutdown. Original symptoms persist. Backlights flick momentarily before PSU shuts down.

                Comment


                  #9
                  Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                  Removed 4.7K ohm resistor. Removed backlight IC801 completely.

                  Power supply does not start up at all. No 5V or 16V output. (5V rail provides ~3V unsteady voltage)

                  Comment


                    #10
                    Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                    So pin 1/3 to common Drain still showing 0 Ohm on board?
                    Never stop learning
                    Basic LCD TV and Monitor troubleshooting guides.
                    http://www.badcaps.net/forum/showthr...956#post305956

                    Voltage Regulator (LDO) testing:
                    http://www.badcaps.net/forum/showthr...999#post300999

                    Inverter testing using old CFL:
                    http://www.badcaps.net/forum/showthr...er+testing+cfl

                    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                    http://s807.photobucket.com/user/budm/library/

                    TV Factory reset codes listing:
                    http://www.badcaps.net/forum/showthread.php?t=24809

                    Comment


                      #11
                      Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                      With Q805 & Q806 installed, I get

                      Q805
                      S1 to drain = 1.4 ohms
                      S2 to drain = 0, dead short.

                      Q806
                      S1 to drain = 1.4 ohms
                      S2 to drain = 0, dead short.

                      With Q805 & Q806 removed from circuit
                      Chip Readings:
                      Q805
                      S1 to drain = Roughly 10 MegOhms, and falling
                      S2 to drain = 0, dead short

                      Q806
                      S1 to drain = 1.4 ohms
                      S2 to drain = DMM reads "OL", open circuit

                      Board itself:
                      Q805
                      S1 to drain = Open
                      S2 to drain = Open

                      Q806
                      S1 to drain = Open
                      S2 to drain = Open
                      (this is understandable, on this board the common drains on each FET connect only to each pin of the inverter xfmr, nothing else)

                      Comment


                        #12
                        Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                        So both MOSFETs (Dual-MOSFET P-CH/N-CH) are shorted out!
                        With Q805 & Q806 removed from circuit
                        Chip Readings:

                        Q805
                        S1 to drain = Roughly 10 MegOhms, and falling
                        S2 to drain = 0, dead short
                        It is bad, shorted.

                        Q806
                        S1 to drain = 1.4 ohms
                        S2 to drain = DMM reads "OL", open circuit
                        It is bad, shorted out.
                        The transfomer is driven by full-bridge setup, that is why it uses 2 dual-MOSFETs (N-CH/P-CH).
                        This will cause the power supply to go into startup/shutdown cycle when the current draw is too much.
                        Attached Files
                        Last edited by budm; 05-12-2016, 11:35 PM.
                        Never stop learning
                        Basic LCD TV and Monitor troubleshooting guides.
                        http://www.badcaps.net/forum/showthr...956#post305956

                        Voltage Regulator (LDO) testing:
                        http://www.badcaps.net/forum/showthr...999#post300999

                        Inverter testing using old CFL:
                        http://www.badcaps.net/forum/showthr...er+testing+cfl

                        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                        http://s807.photobucket.com/user/budm/library/

                        TV Factory reset codes listing:
                        http://www.badcaps.net/forum/showthread.php?t=24809

                        Comment


                          #13
                          Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                          Would anything else on the board cause the shorted MOSFETs? Should I keep looking for a root cause, or replace the MOSFETS and call it fixed (If it works afterwards)?

                          I'll start looking for compatible replacements and return, thanks!
                          Last edited by fuxxy; 05-13-2016, 11:48 AM.

                          Comment


                            #14
                            Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                            More likely the MOSFET just failed due to bad filter caps, as you can see the board around those two MOSFETs have dark color due to the heat from the MOSFETs.
                            Get the new MOSFETs and try.
                            Never stop learning
                            Basic LCD TV and Monitor troubleshooting guides.
                            http://www.badcaps.net/forum/showthr...956#post305956

                            Voltage Regulator (LDO) testing:
                            http://www.badcaps.net/forum/showthr...999#post300999

                            Inverter testing using old CFL:
                            http://www.badcaps.net/forum/showthr...er+testing+cfl

                            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                            http://s807.photobucket.com/user/budm/library/

                            TV Factory reset codes listing:
                            http://www.badcaps.net/forum/showthread.php?t=24809

                            Comment


                              #15
                              Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                              Replaced the two MOSFETs, and display works normally! Thanks for the help, budm.

                              Comment


                                #16
                                Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                                Hey Fuxxy,
                                I apologize for hijacking this thread but I'm a new member and it won't let me message you directly. I have this exact monitor and had to replace some caps myself. I was an idiot though and forgot to take pictures or mark how the pink/white, blue/black wires connect to the board. I know this is a long shot but do you possibly remember, have pictures, any advice? Thanks man!

                                Comment


                                  #17
                                  Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                                  If you mean the wires that connect the ccfl's to the power supply, it does'nt matter which one goes where. each connector goes to one lamp

                                  Comment


                                    #18
                                    Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                                    Originally posted by R_J View Post
                                    If you mean the wires that connect the ccfl's to the power supply, it does'nt matter which one goes where. each connector goes to one lamp
                                    Yep, those are the ones I'm trying to figure out. Why would they have them different colors? Also, the service manual says the pink wires are high voltage and the blue wires are low voltage. Wouldn't that make a difference? Just to make sure I'm not misunderstanding you these are the wires/connections I'm talking about. (These aren't mine, just ones I found on the internet)

                                    http://stewartgreenhill.com/articles...orinterior.jpg

                                    https://www.electronicspoint.com/att...831-jpg.21562/

                                    https://i.warosu.org/data/g/img/0620...3272826722.jpg

                                    Thanks for the quick response so far!

                                    Comment


                                      #19
                                      Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                                      The plugs only go in one way, the low voltage is the thiner wire, each white plug is the same. In these pictures they have on plug with a blue and black wire and another plug with a pink and white wire, I see no difference between them but if you like connect them like the picture, blue/black; pink/white; blue/black; pink/white
                                      If you search Samsung 225bw, you will see them connected with the blue plugs to the outside and the pinks toward the middle, it just does'nt matter.
                                      The manual is only concerned about which wire goes to which pin of the plug, Pin 1 is high voltage, pin 2 is the return LV. Thats if you were replacing the plugs for example
                                      Last edited by R_J; 02-07-2018, 09:47 PM.

                                      Comment


                                        #20
                                        Re: AOC 2236Vw (TFT22W90PS) Blue power light flashing, no video

                                        Originally posted by R_J View Post
                                        The plugs only go in one way, the low voltage is the thiner wire, each white plug is the same. In these pictures they have on plug with a blue and black wire and another plug with a pink and white wire, I see no difference between them but if you like connect them like the picture, blue/black; pink/white; blue/black; pink/white
                                        If you search Samsung 225bw, you will see them connected with the blue plugs to the outside and the pinks toward the middle, it just does'nt matter.
                                        The manual is only concerned about which wire goes to which pin of the plug, Pin 1 is high voltage, pin 2 is the return LV. Thats if you were replacing the plugs for example

                                        Ok cool, that's what I was looking for. I knew they could only hookup one way. I just wasn't sure about the "order" they needed to go in. Sadly it doesn't matter in the end. I'm still having the same issue Fuxxy had. Black screen, blinking blue power. I wouldn't even BEGIN to know how to desolder/solder a mosfet. lol I appreciate everyone's input!

                                        Comment

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