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Dell 2408WFPb / 2408WFP - No Power

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    #21
    Re: Dell 2408WFPb / 2408WFP - No Power

    That post is 12 months old? if you need help tell us what is wrong with your monitor
    what is doing- not doing and post good clear pictures of YOUR boards
    Please upload pictures using attachment function when ask for help on the repair
    http://www.badcaps.net/forum/showthread.php?t=39740

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      #22
      Re: Dell 2408WFPb / 2408WFP - No Power

      Originally posted by bubbs198 View Post
      Did you find the problem with your monitor _
      After letting it sit for 6 months, it started working again for a few months. However, now it's back to doing the same and not turning on.

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        #23
        Re: Dell 2408WFPb / 2408WFP - No Power

        The startup capacitor is C606 also C611 47uf 50V could be defective as also IC701 TL431 as per two of the posters here.

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          #24
          Re: Dell 2408WFPb / 2408WFP - No Power

          Originally posted by viziks View Post
          The startup capacitor is C606 also C611 47uf 50V could be defective as also IC701 TL431 as per two of the posters here.
          OK thanks. I tried replacing both 47uF capacitors. No luck.

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            #25
            Re: Dell 2408WFPb / 2408WFP - No Power

            Did you test the diode mentioned previously
            Please upload pictures using attachment function when ask for help on the repair
            http://www.badcaps.net/forum/showthread.php?t=39740

            Comment


              #26
              Re: Dell 2408WFPb / 2408WFP - No Power

              Originally posted by selldoor View Post
              Did you test the diode mentioned previously
              I tested the diodes with a multimeter and they seemed to check out, unless I'm missing something.

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                #27
                Re: Dell 2408WFPb / 2408WFP - No Power

                i have the same power supply as sparrow, the chip (IC601 AND IC651) were blast due to power over loading.

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                  #28
                  Re: Dell 2408WFPb / 2408WFP - No Power

                  hi

                  Comment


                    #29
                    Re: Dell 2408WFPb / 2408WFP - No Power

                    Hi everybody,
                    I have a Dell 2408 with this problem: everytime when I turn on the monitor, the power led doesn't go on. I have to unplug the power cord and then pluggin, and repeat 3 or 4 time, after that the monitor works well. But after not use about half an hour, the same thing happened.
                    I changed two caps 47mf/50v and the IC KA431 from another power supply board of a Dell 2047 (This Dell 2407 is working, only one thing that I cannot access the menu).
                    Can anyone help me ? Thanks a lot.

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                      #30
                      Re: Dell 2408WFPb / 2408WFP - No Power

                      Hi to All,
                      I am in much the same predicament as Sparrow.
                      I have a very very very basic knowledge of the matter, but thanks to these forums I have successfully repaired several monitors, except for this one...
                      The readings (very basic VOM) seem to quite regular throughout the board (comparing them to previous/other threads except for the diode D701 & D703 which seem to be giving a value regardless of how I place the tester leads on the pins.
                      The only thing I haven't tried is measuring the Vcc value of IC601 as I am not sure how too.
                      I've uploaded some images which I hope are of some use.
                      At this point short of changing all the caps, IC's, shunts, I am not sure of what to do.
                      Thanks in advance for any ideas !
                      Attached Files

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                        #31
                        Re: Dell 2408WFPb / 2408WFP - No Power

                        Hi all,
                        My monitor started not turning on: either the LED was on but the power button did nothing or the LED would blink for a 1/10s when the monitor was plugged in.
                        Initially, I had something around 23VDC on the power board output but also 50VAC superimposed on the output (referenced to chassis). The USB ports were receiving 5V.
                        I've replaced the old TL431 (which tested fine with 1k resistor on a power supply) with another one (also tested) but now I get 65VDC output and a burning smell from the area around R611.

                        All the diodes and transistors were tested, nothing was shorted, nothing seems open.
                        The new TL431 shows 2.65V on the reference terminal when powered on, I was expecting ~2.5V.

                        I don't see any bulging caps and no obvious burn damage.

                        What is the expected output of the voltage supply?
                        What voltages waveforms should I look for?

                        EDIT:
                        Ok, I did some thinking, the TL431 reference si given by Vout going into the R716/R715 divider which means the output will be 2.5V*(1+28/3.32)=23.58V. I've put back the old TL431 and now I'm getting 23.4V on the output with no AC voltage. Still not sure what's happening.
                        Last edited by brainwash; 02-10-2016, 01:37 PM.

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                          #32
                          Re: Dell 2408WFPb / 2408WFP - No Power

                          my 2408 failed, I've applied information shown here to debug it. Seemed like the voltages were OK, symptom was-- plug power cord in and the power LED might flash for 1/2 second, but then stayed off and would not power on. Probing today in the power supply, all seemed OK, voltages normal, then I look down and the green LED is on-- monitor is working. I'm thinking there's a cold solder joint! I'm going to let it run for awhile and see what happens. I guess if there's a repetition, I'll have to disassemble the supply and just reheat all the solder joints.

                          Comment


                            #33
                            Re: Dell 2408WFPb / 2408WFP - No Power

                            Hi All,

                            I know that this post is really old but I found some activity on last days here. I came to this forum with exactly same issue as was described by member nickname Brainwash. On my desk is DELL Ultrasharp 2408WFP. After connection of supply cable green led blinks (not every time !!) and it is all. it is not possible to switch it on. Power source works fine, on output it has 24.5V exactly as reference (TL431) sets. So I can say that root cause is not in switching power supply but very probably in mainboard. I completely checked controll board with buttons and LEDs, flat cable and all is OK. I also checked some supply sources on mainboard and they looks also OK and switching. Also LDOs works fine.

                            I would like to know more about CN701 - is there any feedback from backlight inverter ? Is there power OK signal or something like this ?

                            Do you have any information about mainboard in this DELL monitor ? I would like to find problem.

                            Thanks a lot
                            Radek

                            Comment


                              #34
                              Re: Dell 2408WFPb / 2408WFP - No Power

                              I am also trying to repair a Dell 2408WFPb. I have the same problem as mentioned in one of the previous posts. A led light that blinks one time and the monitor won't turn on. The power supply is OK, because CN701 has about 24V on the output. The reason that the inverter board doesn't power on is simple. The first black wire on CN701 is the ON/OFF signal and it's 0V.

                              I started to suspect the mainboard and I found a way to power up this board. It seems like there are two main sections on it. Each section has a big chip, a crystal and a voltage regulator. First, I measured the section at the side where the power supply cable comes in. The crystal has a perfect sine wave and the voltage regulator shows a perfect 1.8V. But there is no voltage on the second crystal and voltage regulator.

                              I heated the heatsink and the onboard chip in the first section very carefully with a hot air rework station. Then I tried to power up the monitor and it was working great again. I waited some time until the heatsink was cooled down. The monitor did not start up. I heated the heatsink and chip again and the monitor was working fine.

                              I think there is a cold solder joint in one of the pins of this chip. Maybe a reflow precedure will solve the problem, although this method is not very reliable. I hope this post will help other people to troubleshoot this specific problem.

                              Greetz,
                              Erwin
                              Attached Files

                              Comment


                                #35
                                Re: Dell 2408WFPb / 2408WFP - No Power

                                Hi on my Dell 2408WFPb iheard just buzing and screen was on but not worked buttons.. controling etc .. i should change KA431 .. but i tryed measure voltage and i connected via my fault pins 3 and 4 on 1203P60 yes i am idiot ... tip ofd my voltmeter slided and booom !!!

                                fuse T 4A 250V
                                R613 200R
                                R615 R22

                                down ... i changed all, remove 1203P60 and clean mess around from spark ... and when i connect it again ... is fuse and R615 size R22 (220 mOhm) down


                                probably some IC or transistors died any idea where to start?

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                                  #36
                                  Re: Dell 2408WFPb / 2408WFP - No Power

                                  Hi Locki, I think you should check all components around the 1203P60 IC. Thus also the SMD components on the other side of the board (diodes, zener diodes, resistors, etc...). Good luck!

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                                    #37
                                    Re: Dell 2408WFPb / 2408WFP - No Power

                                    2SK3548 is conductive in all combination S G D .... ordered new one! I hope it is this one

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                                      #38
                                      Re: Dell 2408WFPb / 2408WFP - No Power

                                      Ok, but also check some other (SMD) components around the IC that drives the gate of 2SK3548. If there is a faulty one, the 2SK3548 can go down again...

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                                        #39
                                        Re: Dell 2408WFPb / 2408WFP - No Power

                                        The IC that drives the MOSFET should be replaced at this point.
                                        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

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                                          #40
                                          Re: Dell 2408WFPb / 2408WFP - No Power

                                          1203P60 and L6561 are also ordered

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