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Samsung Syncmaster 245b BN44-00195A

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    Samsung Syncmaster 245b BN44-00195A

    Hello people.
    I have the samo problem as described in this thread:
    https://www.badcaps.net/forum/showth...highlight=245b

    The monitor was on standby and one day the screen (or just the backlight) would not turn on. Computer still recognized the monitor and was acting like it was there (5 screen setup). I switched the monitor off with the big switch by the cable, waited 5ish seconds and switched it back on. I heard a loud bang.

    Both fuses blown, resistor blown, bad mosfets.

    I checked most electrolitic caps in circuit and they show correct values.

    I have tried replacing all of that (user IRF840 I had laying arround - please don't judge) and it all blew up again when i turned it on.

    What do you guys suggest I check and should those things be desoldered first?

    Thank you!



    Attached Files

    #2
    Re: Samsung Syncmaster 245b BN44-00195A

    First of all did you remove those brown glues? Those glues become conductive and corrosive and will eat up wires and traces, and since they are conductive it will also damage the circuits.
    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

    Comment


      #3
      Re: Samsung Syncmaster 245b BN44-00195A

      I had removed brown glue. Scraped it off.
      There is some white/yellowish glue on some components. Should I scrape all that off too?

      Comment


        #4
        Re: Samsung Syncmaster 245b BN44-00195A

        So I took out my mosfets and they seem ok out of circuit. I can open and close them with a multimeter.
        The replacement resistor blew.
        The fuses are ok.
        The element marked BM801 is shorted both ways. Not sure what it is.
        I desoldered 3 diodes i suspected conduct, but they all tested ok out of circuit.
        I thought one of optocouplers could be bad but tested ok out of circuit.
        What should I take a look at? Desolder every component and test it?
        At least help me with the best order. Also can IRF840 mosfet replace original ones?

        Comment


          #5
          Re: Samsung Syncmaster 245b BN44-00195A

          BM801 is a ferrite bead on a wire, it acts like an inductor in the circuit, it will check shorted. The IRF840 are not insulated case like the original, so if used without an insulating kit, they will be shorted to the heatsink.
          Last edited by R_J; 08-12-2020, 05:36 PM.

          Comment


            #6
            Re: Samsung Syncmaster 245b BN44-00195A

            Originally posted by R_J View Post
            BM801 is a ferrite bead on a wire, it acts like an inductor in the circuit, it will check shorted. The IRF840 are not insulated case like the original, so if used without an insulating kit, they will be shorted to the heatsink.
            I ordered some isolation pads and nipples as they call them.
            It was stupid to screw mosfets into heatsink without isolation.

            What else could I check? Why would the resistor be blown? I read it as 0,22 Ohm. Should I check anything else before I turn the power back on?
            In case it blows again even with all the goo cleaned up?

            Comment


              #7
              Re: Samsung Syncmaster 245b BN44-00195A

              Isolation kit arrived along with the 0,22/2W resistors.
              I put it all back together with IRF840 as replacements until i get original mosfets.
              I'm back at the biggining now. The power button is illuminated but no picture or light on the LCD. Windows recognize the monitor correctly.
              I tested the connector pins on the powerboard and i cant find any voltage between labeled gnd and 5.3V pins.
              Any bright ideas? It's been a long time since i learned this stuff in highschool, sorry if I sound like an idiot. :-)

              Comment


                #8
                Re: Samsung Syncmaster 245b BN44-00195A

                Originally posted by Mandor View Post
                Isolation kit arrived along with the 0,22/2W resistors.
                I put it all back together with IRF840 as replacements until i get original mosfets.
                I'm back at the biggining now. The power button is illuminated but no picture or light on the LCD. Windows recognize the monitor correctly.
                I tested the connector pins on the powerboard and i cant find any voltage between labeled gnd and 5.3V pins.
                Any bright ideas? It's been a long time since i learned this stuff in highschool, sorry if I sound like an idiot. :-)
                Please look at the schematic (https://cdn.badcaps-static.com/pdfs/...f8a620fd8c.pdf) of the board.

                1) Make sure the RM801 (0.22 Ohms) is still good.

                2) The power button is illuminated means 5.2VSTB on connector CNM801 pin 3 is present.

                3) The switched 5.3V, 12V, 13V, and 24V will not be present until main board sends the ON/OFF (PS-ON, connector CNM801 pin 1) of >2V (>2V = ON, <1V = OFF) to turn on those switched power supplies when power switch is activated to turn on the monitor. The ON/OFF signal also turns on the PFC Voltage booster circuit so you need to check the DCV between the two legs of the main 450VDC filter cap if it has about 380 ~ 400VDC or not. So verify that the ON/OFF (PS-ON) is present.

                4) if the ON/OFF control is present, and the Boosted PFC Voltage is present, then check the capacitance of this common failure cap CM808 (blue rectangular cap) on this board, you need to remove it to test it off the board.
                Last edited by budm; 08-14-2020, 01:12 PM.
                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

                Comment


                  #9
                  Re: Samsung Syncmaster 245b BN44-00195A

                  I think my board is a little bit different.
                  I Found the connector CN851 with fewer pins which has PSON and S_B. S_B has 5.23V.
                  The big electrolytic cap has 317V on it.
                  The only blue rectangular cap is CM812 12nJ630V measured out of circuit 12nF.
                  The new 0.22Ohm resistor measured in circuit 0.22 Ohm.

                  How do I go about verifying that PS_ON is present? PSON pin is 0.3V. I tried shorting S_B and PSON pins but big cap is stil 317V and not 380V and there is no voltage on 24V/5V pins.


                  Attached Files

                  Comment


                    #10
                    Re: Samsung Syncmaster 245b BN44-00195A

                    You must disconnect the cable between the main board and the power supply board when forcing on the power supply or you may damage the mainboard.
                    With the cable connected, you should see the PSON pin go from .3v to 3~5v whenthe power button is pressed, ifit does'nt it is likely the mainboard is not sending the command.
                    With the mainboard/power supply cable disconnected, connecting S_B to PSON should turn on the power supply. if not you still have a problemonthe power supply board.
                    Check the voltage across CB806, it should be around 20vdc, then check the voltage across CP811, it should be around 16vdc when the power supply is forced ON.

                    Comment


                      #11
                      Re: Samsung Syncmaster 245b BN44-00195A

                      I disconnected the cable.
                      Put a little switch between S_B and PSON.
                      CB806 is missing, like it was never installed. I measure 266Vdc between the pads when switch is OFF and 310 when switch is ON.
                      CP811 I can't find. I guess the ICP801S is the SMD part on the back. If I measure PIN8 of SMD dip to the ground (minus on graetz), switch OFF reads 0Vdc and ON reads 10Vdc.
                      Attached Files

                      Comment


                        #12
                        Re: Samsung Syncmaster 245b BN44-00195A

                        I still don't know what to do.

                        Comment


                          #13
                          Re: Samsung Syncmaster 245b BN44-00195A

                          Check the voltage across CP804, this is the VCC for ICM801, (what is the number on ICM801)? is it MC33067?
                          The VCC should be on JB816 (use Hot ground to check this voltage)
                          Last edited by R_J; 09-09-2020, 10:54 AM.

                          Comment


                            #14
                            Re: Samsung Syncmaster 245b BN44-00195A

                            ICM801 is MC33670P.
                            Positive side of CP804 is 10.43V relative to negative lead of big high-voltge cap. cap. It connects to VCC of ICP801S (pin 8) vis J806. ICM801 is on the other side of the board. ICM801 on it's VCC (pin 15) also has 10.39V. So i guess they are connected.
                            I think the jumper you are refering to is J816 on my board, not JB816.
                            I do have IRF840 insted original mosfets. The new 9N50C parts did arrive from Mouser but I don't know If I waant to risk blowing them yet.

                            Comment


                              #15
                              Re: Samsung Syncmaster 245b BN44-00195A

                              I can't find anything for a mc33670p it must be a mc33067, the vcc seems to be too low for the ic to operate, I meant J816. It could be that the small capacitors for the vcc line are bad (as in open) and not charging to the full vcc voltage. Caps like Cp804 and the one below it, Cp809
                              Last edited by R_J; 09-20-2020, 10:07 AM.

                              Comment


                                #16
                                Re: Samsung Syncmaster 245b BN44-00195A

                                I took most of the electrolytic caps out and measured them and they all seemed fine on capacity test. Should i test in another way?
                                Attached Files

                                Comment


                                  #17
                                  Re: Samsung Syncmaster 245b BN44-00195A

                                  Replace the ones on the VCC supply, Testers can show that the capacity is ok but in circuit they don't work

                                  Comment


                                    #18
                                    Re: Samsung Syncmaster 245b BN44-00195A

                                    Originally posted by R_J View Post
                                    Replace the ones on the VCC supply, Testers can show that the capacity is ok but in circuit they don't work
                                    Replaced all the electrolytic ones except the biggest one.
                                    Nothing changed.

                                    Comment


                                      #19
                                      Re: Samsung Syncmaster 245b BN44-00195A

                                      I also put in a new pair of correct mosfets. ICM801 and ICP801s still have 10.4V

                                      Comment


                                        #20
                                        Re: Samsung Syncmaster 245b BN44-00195A

                                        So I'm looking at datasheet for TDA4863 and it says VCC should be Vz 18-22V. It's called zenner voltage. Great. So i try to find a zenner diode in the circuit diagram. There it is right above the chip. DZP801, part number BZX84C18 and it should be 18V according to datasheet. So i thought i'd check that.
                                        But I have two diodes on the actual board. DZP801 and DZP802 and they are P6KE300A and have 140V and 210V on them.
                                        OK DZP801 kathode should be on pin 7 of the IC. I can only see gate of QP801S via resistor.
                                        I'm just lost and the schematic is not correct or I can't read it.
                                        Oh and I also reflown solder on most ICs and Transistors.
                                        Last edited by Mandor; 10-17-2020, 04:47 AM.

                                        Comment

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