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Dell E177FPf No Power

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    #41
    Re: Dell E177FPf No Power

    Good board: 806
    Bad board: 574

    Note: good board currently doesn't have transformer T850 connected. Also I850 and U850 are removed. I've placed these on the bad board... just wanted to state that in case it affects the readings (not sure how it would, but just to be safe).

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      #42
      Re: Dell E177FPf No Power

      Originally posted by billy66 View Post
      Here is what I've done:

      - Recapped entire secondary side... no changes
      Does this include recapping C857?
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        #43
        Re: Dell E177FPf No Power

        Yes. C857 is a 10uf50V. Replaced with Panasonic FC.

        Comment

          #44
          Re: Dell E177FPf No Power

          Originally posted by billy66 View Post
          Good board: 806
          Bad board: 574
          And if you reverse the probes to test the other direction, do you get "1" or OL?

          That is, put your multimeter on diode test function. Put red probe on one side of diode and black probe on the other. Record measurement. Now put switch the probes and record the measurement.
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            #45
            Re: Dell E177FPf No Power

            On both boards, if you put the probes the other way, you get 1... OL

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              #46
              Re: Dell E177FPf No Power

              Okay, looking at



              page 12 shows a reference circuit.

              Pin 3 is VIN. It is "fronted" by R5 and R7 which are 750K ohm 1/4W resistors.

              R5 and R7 correspond to R854 and R853 (marked 754) on your board (I think). Measure both on the ohm scale to see if you get around 750K ohms.
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                #47
                Re: Dell E177FPf No Power

                Bad board: 700K ohm each
                Good board: 750K ohm each

                The bad board took a long time to read. When I first put the probes on the resistor, it would climb up slowly till it stopped around 700K ohms +/- 5k ohm

                Comment

                  #48
                  Re: Dell E177FPf No Power

                  Originally posted by billy66 View Post
                  Bad board: 700K ohm each
                  Good board: 750K ohm each

                  The bad board took a long time to read. When I first put the probes on the resistor, it would climb up slowly till it stopped around 700K ohms +/- 5k ohm
                  Risking a from PlainBill, R854 and R853 form a voltage divider. They drop the voltage from the bridge rectifier (120V x 1.4) to something that feeds into the VIN pin 3.

                  edit: I should point out reading and intrepreting schematics is still a learning process for me. I still have the chicken and egg conundrum when following all the various circuit paths.

                  edit2: I don't know if 700K versus 750K is enough of a variance to say the SMD resistors are bad. 50k/750K is 6.67% variance.

                  edit3: The max for VIN is 30V according to the datasheet. So 25V on pin 3 is within spec.
                  Last edited by retiredcaps; 11-08-2010, 05:19 PM.
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                    #49
                    Re: Dell E177FPf No Power

                    From my still learning schematic reading, all the components that feed into pin 7 VDD are as follows.

                    It looks like D856 is D4, R887 is R12 (reference to page 12 of SG5841 circuit). R887 is 0 (zero) ohm resistor so it should read close to that on your multimeter.

                    C9, I think, is C856 (Panasonic FC 10uF, 50V).

                    You say the U850 replacement is a known good one as well.

                    I'm out of ideas right now.
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                      #50
                      Re: Dell E177FPf No Power

                      Originally posted by billy66 View Post
                      Yes. C857 is a 10uf50V. Replaced with Panasonic FC.
                      Well it doesn't happen often but it is possible to receive parts that are packaged wrong
                      Did you verify with your eye ball that C857 was indeed 10uf and not something else?
                      Al.
                      Whatever I do, I consider it a success, if in the end I am breathing, seeing, feeling and hearing!

                      Comment

                        #51
                        Re: Dell E177FPf No Power

                        Al. Yeah, I doubled checked after retiredcaps asked. It is so easy to mess those up.

                        Retiredcaps.... the U850 is from the known good board. At risk of sounding like a moron, it is possible I mixed up the two chips when swapping? And put the bad one back on? It's a chance... I'll have to remove and replace again. This will take a bit, as desoldering those and removing SUCK...

                        Comment

                          #52
                          Re: Dell E177FPf No Power

                          Originally posted by billy66 View Post
                          Retiredcaps.... the U850 is from the known good board. At risk of sounding like a moron, it is possible I mixed up the two chips when swapping? And put the bad one back on? It's a chance... I'll have to remove and replace again. This will take a bit, as desoldering those and removing SUCK...
                          I can't think of anything else. So if you want to change U850, go ahead. Use a sharpie and mark the U850 chip so you don't get them mixed up.

                          These videos from CuriousInventor + ChipQuik make soldering/desoldering SMD easy.

                          http://www.youtube.com/user/CuriousI...33/3NN7UGWYmBY
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                            #53
                            Re: Dell E177FPf No Power

                            Excellent video. The ChipQuik solder is nice... I'll need to pick some up, as desoldering was a royal pain in the a&&! I've managed to slightly lift one of the connections on the good board when removing the chip... not enough to ruin the board, but I knew if I continued on that path, it would eventually ruin it. I'll hold off on swapping the U850 until I can pick some up...

                            Thanks for the tip. I've read on here before how people suggest ChipQuik to other people, but I've never needed it so I never looked it up. I honestly thought it was going to be some piece of equipment like a special soldering iron.

                            Thanks again.

                            Comment

                              #54
                              Re: Dell E177FPf No Power

                              I swapped out U850 with the other one. Same readings... So both U850s give same readings. I marked them this time, so no possible mix up.

                              Any other ideas?

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