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Acer X233H LCD no power

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    Acer X233H LCD no power

    Hello everyone,

    Yesterday one of my monitors just completely turned off when I was using it. No power, no lights or anything. I tried unplugging it and plugging it back in at first to see if something was wrong with the power cable but still nothing. I then changed cables and changed outlets and nothing as well. I then decided to take it apart and check the boards inside to see if I could see anything wrong. After my own investigation, I couldn't see anything wrong or blown so I decided to come here for help.

    I took some pictures of the board so hopefully someone here can see or help with whats wrong. Thanks!
    Attached Files

    #2
    Re: Acer X233H LCD no power

    do you have a meter?

    Comment


      #3
      Re: Acer X233H LCD no power

      I do. What should I test?

      Comment


        #4
        Re: Acer X233H LCD no power

        One of the first things in the manual (Can be found here page 30) says to measure U703 pin 2. When I measure, I get a solid 0V. Does this mean that this is the problem? I've attached a picture of where I have tested.
        Attached Files

        Comment


          #5
          Re: Acer X233H LCD no power

          Assuming you have checked fuses and they are OK, I would do a very quick test on D805 and D806, on the PSU board,and ensure neither are short cct.It may save you a lot of time.

          Comment


            #6
            Re: Acer X233H LCD no power

            I checked the three fuses on the power board and they gave me correct readings. I tested the two Diodes at the top, D806 and D804, as well as the other diodes on the power board and they all seem to give appropriate readings, anywhere from .55 to .41.

            Comment


              #7
              Re: Acer X233H LCD no power

              Anybody have any suggestions?

              Comment


                #8
                Re: Acer X233H LCD no power

                What DCV do have measured at the two legs of that main filter cap?
                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


                  #9
                  Re: Acer X233H LCD no power

                  Sorry I am not an expert on any of this type of stuff so I am guessing when you say main filter cap you meant the big capacitor right in the middle of the first picture labeled c804?

                  With it plugged in I got a reading of 169V DC.

                  Comment


                    #10
                    Re: Acer X233H LCD no power

                    "With it plugged in I got a reading of 169V DC" That is good.

                    OK, check the MOSFETs in the inverter circuit U501, U502 Source and Drain pin to see if the show low RESISTANCE readings.
                    BTW, I can only see two fuses on the power supply board, the white fuse for the AC main, and red fuse by the white connector for the main board power.
                    Also check the power supply board without connection to the main board to see if you do get any DCV on the secondary side filter caps.
                    Last edited by budm; 02-24-2015, 01:24 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


                      #11
                      Re: Acer X233H LCD no power

                      Sorry, when I read fuses in the previous post I actually checked the resistors. I just checked the red and white fuse with a continuity test and they both seem to be okay.

                      I disconnected the power supply board from the main board and put power to it. I checked the five brown caps and the two green caps and I got 0V DC for all of them.

                      Testing u501 and U502, I connected the ground to the left pin which I believe to be ground. On pin 2(Vout) I got 2.6Mohms and on pin 3(Vin) I got for 34.2kohms both u501 and u502
                      Last edited by ooober60; 02-24-2015, 02:34 PM.

                      Comment


                        #12
                        Re: Acer X233H LCD no power

                        They are power MOSFET with GATE, Drain, and Source pin. There is no Vin, Vout, Gnd pins on MOSFET.
                        So check the resistance between Source and Darin pin.
                        Looking at it with big tab up:
                        Left = Gate
                        Middle (same as the tab) = Drain
                        Right = Source
                        Last edited by budm; 02-24-2015, 03:11 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: Acer X233H LCD no power

                          Sorry. Like I said, this is all new to me. If I did this correctly, I got 2.473 Mohm on u502 and 2.410Mohm on u501 between source and drain pins resistance.

                          The picture is what I did
                          Attached Files

                          Comment


                            #14
                            Re: Acer X233H LCD no power

                            So I've check everything I can but I still can't figure out what wrong. I'm clearly missing something here.

                            Comment


                              #15
                              Re: Acer X233H LCD no power

                              Should I just replace all of the caps and hope for the best? Doesn't seem to be too expensive.

                              Comment


                                #16
                                Re: Acer X233H LCD no power

                                Suggest you test Q804 mosfet mounted on heatsink next to large cap C804. Check it for shorts.

                                Comment


                                  #17
                                  Re: Acer X233H LCD no power

                                  When testing these things, do I need to unsolder them and take them out of circuit? Or does testing them as is work also. The only reason I ask is because when looking up videos on how to test them, the videos always have the components alone and not in any type of circuit.

                                  Comment


                                    #18
                                    Re: Acer X233H LCD no power

                                    With power off, test it as is. If you see a short, remove it and test again to verify your reading.

                                    Comment


                                      #19
                                      Re: Acer X233H LCD no power

                                      OK, check the resistor R815 (Source resistor for Q804) to see if it does show <1 Ohms.
                                      Check clamping Zener diode ZD803.
                                      Check startup cap C807 capacitance and the ESR.
                                      Check the DC Voltage betwen to two leg of that startup cap C807.
                                      Also get the P.N of the SMPS IC802.
                                      Last edited by budm; 02-28-2015, 09:23 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


                                        #20
                                        Re: Acer X233H LCD no power

                                        Q804 Mosfet seems to be okay testing it with a multimeter
                                        Resistor R815 shows right around .9 ohms
                                        When testing the zener diode ZD803, I am getting 0L resistance in one direction and 2.683Mohms in the other direction. According to this website, http://www.learningaboutelectronics....-a-zener-diode, there is a high resistance in both directions and that is is bad. Could this be the problem?

                                        Edit: after doing some further research, http://www.elexp.com/electrical_measurements_part3.aspx, this says to use the diode function on the multimeter. This way, I am getting exactly what it says I should be getting. An open circuit one way, and a reading around 600 in the other direction. So now I am confused. Which way is correct?
                                        Last edited by ooober60; 03-08-2015, 02:17 PM.

                                        Comment

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