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CTX S800BJ Blows Fuse

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    #1

    CTX S800BJ Blows Fuse

    Just closing case on Samsung 215TW (see thread re 1 sec off) when CTX S800BJ went blank. this time more classic symptoms. I could see display under side lighting conditions and at least one cap on power supply showed bulge. I replace cap 813 on power supply (3300 microfrads) and C5 on inverter board (150 microfarad). while testing I managed to short power supply board to case so also replaced fuse. Just put it all back together and have blown 4 replacement fuses. First suspect is wrong fuse. Board calls out T2.5A/250V. I couldn't find slow blow at local Radio Shack so tried standard 2.5 A/250 v Buss fuse. smoke. Power supply is JT186P11/S11. That shows up as a Jean Monitor on Google.

    Any ideas?
    Tags: None
    #2
    Re: CTX S800BJ Blows Fuse

    Originally posted by PineCreek View Post
    Just closing case on Samsung 215TW (see thread re 1 sec off) when CTX S800BJ went blank. this time more classic symptoms. I could see display under side lighting conditions and at least one cap on power supply showed bulge. I replace cap 813 on power supply (3300 microfrads) and C5 on inverter board (150 microfarad). while testing I managed to short power supply board to case so also replaced fuse. Just put it all back together and have blown 4 replacement fuses. First suspect is wrong fuse. Board calls out T2.5A/250V. I couldn't find slow blow at local Radio Shack so tried standard 2.5 A/250 v Buss fuse. smoke. Power supply is JT186P11/S11. That shows up as a Jean Monitor on Google.

    Any ideas?
    When you shorted the power supply to the case the overload shorted a component which blows the fuse. Likely candidates include the bridge rectifier and the power FET.

    PlainBill
    For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

    Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

    Comment

      #3
      Re: CTX S800BJ Blows Fuse

      Originally posted by PineCreek View Post
      Just closing case on Samsung 215TW (see thread re 1 sec off) when CTX S800BJ went blank. this time more classic symptoms. I could see display under side lighting conditions and at least one cap on power supply showed bulge. I replace cap 813 on power supply (3300 microfrads) and C5 on inverter board (150 microfarad). while testing I managed to short power supply board to case so also replaced fuse. Just put it all back together and have blown 4 replacement fuses. First suspect is wrong fuse. Board calls out T2.5A/250V. I couldn't find slow blow at local Radio Shack so tried standard 2.5 A/250 v Buss fuse. smoke. Power supply is JT186P11/S11. That shows up as a Jean Monitor on Google.

      Any ideas?

      What component were you testing when you shorted the power supply and produced the magic smoke? Or, what component was closest to the spot where the short occurred? That and surrounding components would be the primary suspects to check for shorts.
      Last edited by jetadm123; 11-24-2010, 08:20 PM.

      Comment

        #4
        Re: CTX S800BJ Blows Fuse

        From what I see on the board, contact was from what looks like a heat sink to the chasis. I've looked the board over several times and gone through the maneuvers I was making when the short occured and that seems like the most likely contact. It also seems unusual to me as I thought that heatsink would be grounded. I'm flying blind on this one as I haven't been able to secure a set of schematics. Looks like I need to get you folks some good pics. I'll read up on your procedures for adding pics and get them to you as soon as I can.

        Comment

          #5
          Re: CTX S800BJ Blows Fuse

          If the transistor or diode that's mounted to the heatsink has a metal tab, use your DMM (set on resistance) to check for continuity between that metal tab and the heatsink. Normally, the semiconductor manufacturer will internally connect that metal tab to one of the legs (usually middle leg) of that device. So, if it has connectivity to the heatsink, then you may have shorted out that device. Check it for shorts.

          Comment

            #6
            Re: CTX S800BJ Blows Fuse

            Pics attached.
            I replaced original C813 due to bulge.
            Heatsink at right side of top side pic was not firmly soldered to board. I retouched four connections to board.
            Inadvertant contact was between the left top attachment pin for the middle heatsink and chasis of monitor. Note some blackening of the pin in pic of board back (upper middle).
            Component on middle heatsink (the one that I shorted to chasis) has four leads. I presume it is a bridge rectifier. No metal tabs that I could see, but attachment screw passes through component and heat sink. I have not yet measured continuity.
            Two each components on right heatsind have three leads each.
            Attached Files

            Comment

              #7
              Re: CTX S800BJ Blows Fuse

              Originally posted by PineCreek View Post
              Pics attached.
              Great focused pics. Making helping a lot easier.

              Component on middle heatsink (the one that I shorted to chasis) has four leads. I presume it is a bridge rectifier.
              Bridge rectifiers are normally identified on the PCB as BDxyz. In your case, the four diodes D810, D811, D812, and D813 function as the bridge rectifier.

              The component on the middle heatsink with 4 leads is I801 and likely some sort of power MOSFET. From all the boards I have seen, bridge rectifiers are not normally mounted onto a heat sink (they are free standing).

              The diodes or mosfet could be shorted. To test diodes and mosfets (post #13 section 2 for mosfet and post #14 section 7.3), see

              https://www.badcaps.net/forum/showthread.php?t=10419
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                #8
                Re: CTX S800BJ Blows Fuse

                from the description, it DOES sound like a bridge rectifier, because they typically have a hole right through the middle

                Comment

                  #9
                  Re: CTX S800BJ Blows Fuse

                  Retiredcaps identified the components correctly. Note that the heat sink is connected to one side of the main filter cap. This configurations is known a a live (or hot) ground. At least one of D810, D811, D812, and D813 is shorted. I would replace all of them, they have been stressed repeatedly by the surges that blew the fuse.

                  PlainBill
                  For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                  Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                  Comment

                    #10
                    Re: CTX S800BJ Blows Fuse

                    Originally posted by PineCreek View Post
                    I replaced original C813 due to bulge.
                    One other thing. This lcd was made in 2002.

                    It is likely probable that all the remaining caps, regardless whether they are bulging or not, are likely near the end of their useful lifetime. Over time, caps dry out from heat.

                    So, after you figure out what is shorted, many here will suggest you recap all the caps with low esr choices.
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                      #11
                      Re: CTX S800BJ Blows Fuse

                      Got it. Thx folks for helping on turkey day. I'll get on this tomorrow as I've run out of excuses for being away from guests.

                      Thx

                      Comment

                        #12
                        Re: CTX S800BJ Blows Fuse

                        Originally posted by PineCreek View Post
                        Thx folks for helping on turkey day.
                        Turkey day in Canada passed. I'm trying NOT to look at your black friday sales because it just makes me mad how some items are unjustifiably 2x to 4x more expensive in Canada.
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                          #13
                          Re: CTX S800BJ Blows Fuse

                          Even if its half as much here, its still more than I can afford, hence the long man-hours spent on an eight year old monitor.

                          Have a good one.

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                            #14
                            Re: CTX S800BJ Blows Fuse

                            To avoid blowup of fuses, put an electric light bulb instead of a fuse.
                            Use 100W bulb. if it lit brightly and stays like that for a long time, somthing is still shorted.

                            Comment

                              #15
                              Re: CTX S800BJ Blows Fuse

                              Two out four of the bridge diodes were bad. I've ordered new ones. Let you know how it turns out.

                              Comment

                                #16
                                Re: CTX S800BJ Blows Fuse

                                Unit up and running. All told,I replaced all four of rectifier diodes, C5 on inverter board and C813 on power supply. Its working fine. Thx again to all who helped.

                                Comment

                                  #17
                                  Re: CTX S800BJ Blows Fuse

                                  Good work! Glad you got it working!

                                  Comment

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