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    #21
    Re: Viewsonic VX2255WMB Grey Screen

    If you scroll up youll see the results, they were reported to be working properly.

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      #22
      Re: Viewsonic VX2255WMB Grey Screen

      Originally posted by tieny View Post
      If you scroll up youll see the results, they were reported to be working properly.
      It may be me but I dont see them?
      Retiredcaps and I are talking about the connector pins between the power board and the logic board - 4 pins I think CE102?.

      You will need it powered up for this. I also notice that in the pics the boards appear to on the metal frame of the monitor? Do not have it touching like that when powered up and do not put down on metal for at least five minutes after its been powered up (Preferably not at all)
      Please upload pictures using attachment function when ask for help on the repair
      http://www.badcaps.net/forum/showthread.php?t=39740

      Comment

        #23
        Re: Viewsonic VX2255WMB Grey Screen

        There are actually 8 pins from the power connectors

        pin1: -0.0005V pin2: -0.0005V
        pin3: -0.0005V pin4: 5.12V
        pin5: 5.12V pin6: 5.12V
        pin7: -0.0005 pin8: 3.24V


        For the Transformer the combination of pins 1, 4, 5, 8 gave no readings.
        combinations of pins 2, 3, 6, 7 gave all readings from 0.4, 0.5, and 0.6
        Attached Files

        Comment

          #24
          Re: Viewsonic VX2255WMB Grey Screen

          Originally posted by tieny View Post
          There are actually 8 pins from the power connectors

          pin1: -0.0005V pin2: -0.0005V
          pin3: -0.0005V pin4: 5.12V
          pin5: 5.12V pin6: 5.12V
          pin7: -0.0005 pin8: 3.24V
          1) The inverter section typically uses 12V or more. Without this voltage the backlight will never come on.

          2) I circled the 2 output diodes. One will be 5V and the other should be 12V or more.

          3) Put your multimeter on DC volts (20V if manual). Plug in the lcd and power it on. Put your black probe on a ground screw. Put your red probe on the middle pin of each red circled diode. Report the readings and see if they are stable or not.

          4) Indicate in the diagram which diode is 5V so we know which is which.
          Attached Files
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            #25
            Re: Viewsonic VX2255WMB Grey Screen

            5) See if these two mosfets (yellow) are shorted or not. My 2 seconds to black guide has the procedures for testing shorted mosfets.

            6) On the back of the pcb, there is a smd fuse marked "P" (just below the 16 multipin IC). See if it is open. It is probably okay, but let's get confirmation. Refer to guide again.
            Attached Files
            Last edited by retiredcaps; 02-11-2012, 07:13 PM.
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              #26
              Re: Viewsonic VX2255WMB Grey Screen

              I tested both diodes and got readings of 20.3V and 5.12V
              Attached Files

              Comment

                #27
                Re: Viewsonic VX2255WMB Grey Screen

                I'm getting the same values for each of the mosfets.

                measuring pins 1 and 2, won't give me a reading no matter how high i raise the range
                measuring pins 1 and 3, gives me 0.823 on the 2K range
                measuring pins 2 and 3 gives me 0.302 on the 2K range

                The P smd fuse had a reading of 0.4 ohms so its still working.

                Comment

                  #28
                  Re: Viewsonic VX2255WMB Grey Screen

                  Originally posted by tieny View Post
                  I tested both diodes and got readings of 20.3V and 5.12V
                  Recheck your readings on those 8 pins. At least one of them should be close to 19 or 20V.
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                    #29
                    Re: Viewsonic VX2255WMB Grey Screen

                    nope, I rechecked and still have the same values.

                    Comment

                      #30
                      Re: Viewsonic VX2255WMB Grey Screen

                      I spy with my little eyes, F101 (SMD "Y") on the backside of the pcb just below those 8 connectors. See if it is open.

                      PS. This is why clear focused photos are so important.
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                        #31
                        Re: Viewsonic VX2255WMB Grey Screen

                        Doesn't seem to be open, I got a reading of 0.4 ohms

                        Comment

                          #32
                          Re: Viewsonic VX2255WMB Grey Screen

                          Okay, for all the components circled in green, measure the DC voltage of each. For caps, put red probe to positive and black probe to negative. Report all the voltages.
                          Attached Files
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                            #33
                            Re: Viewsonic VX2255WMB Grey Screen

                            And this should be done while plugged off correct?

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                              #34
                              Re: Viewsonic VX2255WMB Grey Screen

                              For voltage readings, the lcd is plugged in and turned on.

                              Resistance measurements are always done with power off and lcd unplugged.

                              If you have to flip the board over to make voltage measurement, use a piece of cardboard as an insulator.
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                                #35
                                Re: Viewsonic VX2255WMB Grey Screen

                                The ones circled in Red I got voltages of 20.3V and the ones in Blue I got voltages of 5.12V
                                Attached Files

                                Comment

                                  #36
                                  Re: Viewsonic VX2255WMB Grey Screen

                                  edit: I did find a schematic at



                                  page 59 shows CN801 and the pinouts. It doesn't show the inverter voltages on the CN801 so it must be right then?
                                  Last edited by retiredcaps; 02-12-2012, 03:10 AM.
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                                    #37
                                    Re: Viewsonic VX2255WMB Grey Screen

                                    Originally posted by tieny View Post
                                    For the Transformer the combination of pins 1, 4, 5, 8 gave no readings.
                                    combinations of pins 2, 3, 6, 7 gave all readings from 0.4, 0.5, and 0.6
                                    1) Take a look at this diagram.

                                    http://lcdparts.net/TransformerDetai...ProductID=3359

                                    2) Set your multimeter to 2000 ohm scale if it manual.

                                    3) Measure the resistance (power off, lcd unplugged) between S1 and S2. Do the same for S3 and S4.

                                    4) Regarding the "no readings". A multimeter always gives a reading. If it shows "1" on the left hand side, it is telling you that the value is out of range or infinity for your chosen ohm setting.

                                    5) BTW, this is unlikely to be your problem as PlainBill gave more plausible reasons. I just wanted to make sure you understand how to properly test this transformer.

                                    6) For the tcon panel, you will have to post a picture of it. It is the board that is near the top of your lcd probably underneath a metal shield.

                                    7) The tcon usually has a SMD fuse. It could be open and causing your white/grey screen.

                                    8) Reseat and clean the tcon connection as well.
                                    Last edited by retiredcaps; 02-12-2012, 03:26 AM.
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                                      #38
                                      Re: Viewsonic VX2255WMB Grey Screen

                                      Originally posted by retiredcaps View Post
                                      edit: I did find a schematic at



                                      page 59 shows CN801 and the pinouts. It doesn't show the inverter voltages on the CN801 so it must be right then?
                                      @retiredcaps. Hi - You've lost me there- what must be right?
                                      Also the schematic shows a different Power board- is that relevant? see pic. On Page 57 it says something about changed values for caps and resistors on Panel Enable circuit which I thought might apply but as I dont really understand schematics thought i'd ask see pic
                                      Attached Files
                                      Please upload pictures using attachment function when ask for help on the repair
                                      http://www.badcaps.net/forum/showthread.php?t=39740

                                      Comment

                                        #39
                                        Re: Viewsonic VX2255WMB Grey Screen

                                        Originally posted by selldoor View Post
                                        @retiredcaps. Hi - You've lost me there- what must be right?
                                        I was thrown off by the negative voltages reported on the connector in post #23. Some of the questions regarding multimeter usage also led me to think that the negative readings were incorrect.

                                        That led to all those voltage measurements on the caps and diodes to verify that the voltage for the inverter section was actually stable and existed.

                                        Also the schematic shows a different Power board- is that relevant? see pic. On Page 57 it says something about changed values for caps and resistors on Panel Enable circuit which I thought might apply but as I dont really understand schematics thought i'd ask see pic
                                        Reading and understanding schematics is still something I'm learning so I don't know why the changed values. Maybe they found that the original specifications were failing under load?
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                                          #40
                                          Re: Viewsonic VX2255WMB Grey Screen

                                          Thanks - got it now.
                                          Please upload pictures using attachment function when ask for help on the repair
                                          http://www.badcaps.net/forum/showthread.php?t=39740

                                          Comment

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