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Need help DCLCD 19" LCD Monitor - I already replaced caps

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    #101
    Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

    Originally posted by DJM_PHX View Post
    I also measured the 22uF cap with a Fluke and it returned 21.7uF.
    uF may be correct, but ESR (ohms) may be too high. I don't know of any Fluke that will measure ESR.
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      #102
      Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

      Thanks. I was suprised that ours read uF's. I know we do not have one that returns ESR.

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        #103
        Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

        I just saw that our HP4284A's can measure ESR. Now I just need to find some leads to use.

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          #104
          Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

          Originally posted by DJM_PHX View Post
          I am waiting for my 22uF caps to come in so in the mean while, I was reflowing the solder on the connector and the transformers as you suggested to others.

          On the SOIC-8 PWM chip, I found a single strand of copper wire that looked like it was laying between the two pins where the yellow line off the yellow circle is on the attached pic. I had it under a microscope and when so I brushed it off of the board. It was so small, I couldn't find it on the table. Maybe a failure mode?

          I also measured the 22uF cap with a Fluke and it returned 21.7uF. Hmmm... I don't know about under a load though.
          If that wire was across pins 4 and 5, then it could have shorted the output of the chip to ground. With the wire removed, does the monitor shows any different signs of life?

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            #105
            Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

            Right now I have the 22uF cap out so I can't try it. I may just put it back in and give it a try since the new caps haven't arrived yet.

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              #106
              Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

              I put the cap back in. No difference. I can hear a steady ticking noise that coincides with the voltage pulses mentioned earlier. I seems to be in the area of the yellow transformer or the sink next to it. I can't pinpoint it. Any input on this?

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                #107
                Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                Originally posted by DJM_PHX View Post
                I can hear a steady ticking noise that coincides with the voltage pulses mentioned earlier.
                The ticking is the SMPS controller trying to start up. If the little cap is proven to be bad and replaced with a good one, the ticking will go away.
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                  #108
                  Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                  Ok thanks. I guess I will have to wait until the new cap arrives.

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                    #109
                    Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                    Originally posted by DJM_PHX View Post
                    I guess I will have to wait until the new cap arrives.
                    Where and what brand/series did you order? If USA digikey, most here say it arrives in 2 days or less.
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                      #110
                      Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                      Ok, the 22uF cap is in and no change. The clicking noise is still there. Replace the 100uF large cap next I assume?

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                        #111
                        Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                        I am not even gettiing 1V out of any of the wires on the long connector as listed before, even with the new cap.

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                          #112
                          Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                          Originally posted by DJM_PHX View Post
                          Ok, the 22uF cap is in and no change. The clicking noise is still there. Replace the 100uF large cap next I assume?
                          What did brand and series is the replacement cap?

                          Before replacing the big one, what is the voltage across the 22uF cap?
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                            #113
                            Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                            Originally posted by DJM_PHX View Post
                            I am not even gettiing 1V out of any of the wires on the long connector as listed before, even with the new cap.
                            That is expected because the SMPS still hasn't started (the clicking sound).
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                              #114
                              Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                              Ok. In post #2 on the right circled in green is the power filter caps. behind them are two units connected to the heatsink (in Yellow). Are they power transistors? The top one, on my board, the outer 2 to the center pin only have 0.1 ohms res. The other two have on the board have much greater amounts. That one is directly connected to the large yellow transformer, or is this the SMPS?
                              I have not even a flicker of light from the power LED on the front panel any more.

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                                #115
                                Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                                Originally posted by DJM_PHX View Post
                                Are they power transistors? The top one, on my board, the outer 2 to the center pin only have 0.1 ohms res.
                                The power transistor is just above the big cap in post #2. The two ICs on the heat sink next to all those capacitors on the right are schottky diodes. That reading of 0.1 ohms could be right because it is measured "in circuit". What you are looking comes after the SMPS starts.

                                What is the voltage across the new small cap and is it stable or fluctuating like before?
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                                  #116
                                  Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                                  They were suppose to be Rubycon's but they sent Chengx.
                                  The voltage is not stable and is 10V-15V DC.
                                  Is the large sqr. yellow unit the SMPS?
                                  Why can I detect voltage on the heat sink by the large cap?

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                                    #117
                                    Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                                    retiredcaps, and all, have a Happy New Year.
                                    I'm calling it a day and will pic this up next year. But, if you think of anything else, let me know.

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                                      #118
                                      Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                                      Originally posted by DJM_PHX View Post
                                      retiredcaps, and all, have a Happy New Year.
                                      I'm calling it a day and will pic this up next year. But, if you think of anything else, let me know.
                                      I and probably others will have suggestions. The next post will probably be a long one and I don't have time right now to write it all out.

                                      Any chance of getting the Rubycon? Most here will question the Chengx brand even though the little cap may not root cause here.

                                      If it is not the small cap, please re-measure the large cap to see if the fluctuating voltage is there or not. Other possibilities is that the SMPS controller chip is bad. I'm trying to guide you through each scenario one at a time.
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                                        #119
                                        Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                                        I appreciate it. The large cap V is the same and fluctuating as before. I read that the Chengx brand is not liked. I can try to get a replacement for it. Since I see the same voltages and fluctuation, I for now will leave it in. The board is looking a bit rough at the solder points.

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                                          #120
                                          Re: Need help DCLCD 19" LCD Monitor - I already replaced caps

                                          Originally posted by DJM_PHX View Post
                                          The large cap V is the same and fluctuating as before.
                                          Just to confirm, are all the boards are connected together during these tests?

                                          Okay, I have to leave now and won't be posting until later tonight.
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