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    #1

    Samsung Plasma PN50A550S1F no power

    Hi all, picked up this television and was told by owner that he went to put it on and it wouldn't power up, no lights.
    I found a blown 12amp main fuse and 2 10v 2200uf samwha caps bulged. I have replaced the caps with panasonic FC caps.

    Now i believe i can power up the power supply with every thing disconnected to check voltages on the connectors! However i don't want to waste a fuse or damage the supply by putting power to it prematurely.
    Should i check voltage regulators or anything else before powering up the board.

    I should say that i have managed to fix half a dozen computer screens, just lately an Acer and a Samsung T200 lcd, both with bad caps. previous fixes were with the help of this site and lots of reading.

    Here are some pics. Any help is appreciated.

    Mike
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    #2
    Re: Samsung Plasma PN50A550S1F no power

    Ok, will try the pics again.
    Attached Files

    Comment

      #3
      Re: Samsung Plasma PN50A550S1F no power

      Originally posted by maddog310 View Post
      However i don't want to waste a fuse or damage the supply by putting power to it prematurely.
      Should i check voltage regulators or anything else before powering up the board.
      If the fuse blew, check the bridge rectifier, big filter capacitor and power mosfet to see if they are shorted.
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        #4
        Re: Samsung Plasma PN50A550S1F no power

        Thanks for the reply retiredcaps, i tested the rectifiers by this video, http://www.youtube.com/watch?v=dqkT6hF0O3E

        they test good, DS803 AND DS805, i get a reading one way from - or + to ac, middle pins, nothing between the two middle pins.
        Now testing the large caps, 3 of them? CP810,CP809 and CS813 or just the first two. Do i power up the board and check the voltages and the mosfets your talking about are on the heatsinks. I can test these in circuit in the diode mode on a dmm.

        Mike

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          #5
          Re: Samsung Plasma PN50A550S1F no power

          Across the two largest 400/450V caps, test resistance (power MUST be off.)

          Consider building a "lightbulb tester" - put a lightbulb in place of the fuse. If the lightbulb glows permanently when turned on, there is still a problem. If it flashes or goes dim, then the PSU is probably OK.
          Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
          For service manual, schematic, boardview (board view), datasheet, cad - use our search.

          Comment

            #6
            Re: Samsung Plasma PN50A550S1F no power

            Thanks for the reply Tom66, the two large caps 450wv 330uf read around 33 and 30mohms and decreasing. I have checked them a few times with different results, i guess it depends on the state of charge!

            Tested the two power mosfets on the heatsink, i believe thats what they are, QP801 and QP803. the results were.....

            QP801 S+ D- equals 1.053mohms part#20N60C3, GMN642
            S- D+ equals .820mohms and increasing

            QP803 S+ D- equals 1.051mohms part#20N60C3, GIP648
            S- D+ equals.815mohms and increasing
            The meter i have is a auto ranging.

            I made up a light bulb tester with the blown fuse and a 25 watt bulb, but after more reading, i realized the bulb should be 100 or 200 watts. I am going to make one, what size bulb should i use and do i leave all the boards disconnected from the supply?

            Here is a link to the manual, if it helps or if anyone else needs it.
            http://elektrotanya.com/samsung_f43a.../download.html
            Pics of tester and mosfets i tested.

            Mike
            Attached Files

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              #7
              Re: Samsung Plasma PN50A550S1F no power

              A 25W bulb will do for standby testing, but you need a 100W bulb to try starting up the PSU. TV will not work with it, but it should at least show if there is a fault.

              mohm = Mohm = 1000 kohm?
              Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
              For service manual, schematic, boardview (board view), datasheet, cad - use our search.

              Comment

                #8
                Re: Samsung Plasma PN50A550S1F no power

                Ok, so i will use a 100w bulb, do i connect all the boards to the PS or leave everything disconnected?
                I checked diodes at DB810, DB801, DB802, and DP803........ all tested good. Also checked a few others on the board, they tested good.... reading in one direction.
                What do you think of the values i have in my previous post, good, bad or inconclusive.
                Do you think the 2 blown caps could have caused the fuse to blow, i guess it couldn't be that easy!

                Mike

                Comment

                  #9
                  Re: Samsung Plasma PN50A550S1F no power

                  You need to answer my question:
                  mohm = Mohm = 1000 kohm?

                  before I can tell you if your readings are OK.
                  Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                  For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                  Comment

                    #10
                    Re: Samsung Plasma PN50A550S1F no power

                    Sorry about that, it's Mohms. I didn't realize there was a difference for a small m and a capital M.

                    Comment

                      #11
                      Re: Samsung Plasma PN50A550S1F no power

                      Originally posted by maddog310 View Post
                      Sorry about that, it's Mohms. I didn't realize there was a difference for a small m and a capital M.
                      m= milli. M = mega.
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                        #12
                        Re: Samsung Plasma PN50A550S1F no power

                        Mega ohms suggests the components are not shorted.
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                          #13
                          Re: Samsung Plasma PN50A550S1F no power

                          After doing a search i found this out. The meter i have is from crappy tire, used mostly around the house and on cars, checking voltages and continuity. Will be using it on a sled later today, checking a lighting coil.
                          I just realized it has a transistor function, which i could of used a few years ago on a Benq screen. I tested them with the ohm function as i recall.

                          Enough rambling.............

                          I guess my next step will be to power it up with the light bulb, do i connect all the boards or supply only?

                          Comment

                            #14
                            Re: Samsung Plasma PN50A550S1F no power

                            The transistor function on most multimeters is next to useless, don't bother.
                            Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                            For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                            Comment

                              #15
                              Re: Samsung Plasma PN50A550S1F no power

                              Originally posted by tom66 View Post
                              The transistor function on most multimeters is next to useless, don't bother.
                              In Canada, the choice of a "general" multmeter for the "average joe" is limited to what Canadian Tire, Wal-Mart and Home Depot carry. Even the crappy 830 multimeter is sold for $15 to $20 CDN + taxes.

                              The local electronics store prices their brand name multimeters and most of the merchandise like they have never heard of the Internet or ebay.
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                                #16
                                Re: Samsung Plasma PN50A550S1F no power

                                This is the meter i have.......
                                http://www.canadiantire.ca/AST/brows....jsp?locale=en

                                Upgraded from an analogue meter, if i wanted a better meter i could of went to a jobber joint like Napa or something similar or the electronics store or electrical distributor.
                                For my needs this works.

                                Can anybody tell me if i can power up the PS alone or connect all the boards to it and try the light bulb test?

                                Comment

                                  #17
                                  Re: Samsung Plasma PN50A550S1F no power

                                  Did the light bulb trick, 100 watter with a couple test leads, bulb did not light........ ps only.
                                  I then reconnected everything back together as i had it all apart for cleaning and testing.

                                  Retested with light bulb and it would come on then off in conjunction with the relay clicking on then off.

                                  I put the fuse in, connected a dvd player and started everything up. Red power light come on then the blue light in the middle, heard samsung start up sounds but no pic. Changed the cables around still nothing...... unplugged everything and reseated buffer cables, looked around boards to see if i missed a cable, and i did. So i connected the ribbon cable to the ymain and powered it all up.............. now have a running tv for now.

                                  Changed two caps and a fuse, got lucky.

                                  Thanks to retiredcaps and tom66
                                  Last edited by maddog310; 04-08-2013, 09:44 PM.

                                  Comment

                                    #18
                                    Re: Samsung Plasma PN50A550S1F no power

                                    Originally posted by maddog310 View Post
                                    Changed two caps and a fuse, got lucky.
                                    You may consider changing all the capacitors on the power supply based on the cockroach theory. Even though they may look good, they could be failing.
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