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Samsung Syncmaster 245b BN44-00195A

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    #21
    Re: Samsung Syncmaster 245b BN44-00195A

    ICP801S (TDA4863) VCC is on PIN8. It gets that voltage from the M_VCC line. QB802 is the regulator/switch for this voltage. The source of the voltage is from TB801S,pin5, this is rectified by DB803 and filtered by CB806. The voltage at this point should be around +25vdc.
    When pc801S is turned on by ON/OFF, Pin4&3 supply the +25v to the base of QB802 turning it on, the voltage on QB802 is set by ZDB805 + DB804 This will result in about +16vdc on QB802 emitter.

    P6KE300A is a spike suppressor diode and not for supplying vcc voltage
    The VZ is the internal zener diode for protection on the vcc line, The VCC for the ic to turn ON is minimum 12.5vdc, I suspect it operates around 16VDC, If the VCC drops to 10vdc the ic will turn off.
    Last edited by R_J; 10-17-2020, 10:29 AM.

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      #22
      Re: Samsung Syncmaster 245b BN44-00195A

      Hello. I have been abroad for a few months. Sorry.

      I'm am back at it. I really want to learn something from this.
      I hooked up an osciloscope and point 3 on the pic showed slightly oscilating ~10V. You keep mentioning CB806 and it was not populated on my board. I did buy this monitor used but I don't think anyone was opening it. So i put on 47uF/50V at point 2. The osiloscope pic is from point 2 with the cap in. The voltage is oscilating sawtooth slowly. 2 second period. Looked a bit strange to me, so i took a pic.
      Point 3 has nothing now. No voltage.
      Point 1 is 5.2 standby bridged to PS_ON
      Point 4 is +5 to control board, no voltage.
      I'm lost again...
      Attached Files

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        #23
        Re: Samsung Syncmaster 245b BN44-00195A

        This board must be slightly different, It was hard to read the numbers on your board. If cb806 was not populated then it must not be needed so remove it (it would not have been an electrolytic in that spot). It looks like the cap I refered to would be cb809? QB801 is the vcc regulator/switch ZDB801 is the zener diode in the base of qb801 that sets the vcc voltage. Check the voltage on e,b,c of qb801 using hot ground
        Attached Files
        Last edited by R_J; 04-06-2021, 11:14 AM.

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          #24
          Re: Samsung Syncmaster 245b BN44-00195A

          Check that you still have 5 volt standby, installing a 50v cap in the CB806 location on your version of the board is not good as it is across the full B+ (300vdc). I was using a schematic for the BN-00195A and it's location numbers are different than your version of the board.
          Last edited by R_J; 04-06-2021, 04:53 PM.

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            #25
            Re: Samsung Syncmaster 245b BN44-00195A

            Originally posted by R_J View Post
            Check that you still have 5 volt standby, installing a 50v cap in the CB806 location on your version of the board is not good as it is across the full B+ (300vdc). I was using a schematic for the BN-00195A and it's location numbers are different than your version of the board.
            Removed the cap.
            The S_B is not working. Whole connector is now showing signal on attached picture.
            The board is BN44-00195A.
            Looks like I burned something on the left side.
            Attached Files

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              #26
              Re: Samsung Syncmaster 245b BN44-00195A

              Why don't you download the schematic? I have no idea what the "left side" is. Do you mean the primary or HOT side?
              You likely opened either the main fuse or the fuse resistor that supplies the standby transformer. There is a resistor next to J823? it could be open.
              Last edited by R_J; 04-07-2021, 10:25 AM.

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                #27
                Re: Samsung Syncmaster 245b BN44-00195A

                I don't know where to find the correct schematic. I think the one in this thread is slightly different as I said and you said before. Left what I was referring to is lower left on my latest picture posted, the control board connector side.
                i'm sorry if I seem dumb, that is because I am. It's the first time I tried something like this. I never had to troubleshoot anything near this complex. School projects of 10 components 20 years ago is my experience.

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                  #28
                  Re: Samsung Syncmaster 245b BN44-00195A

                  The schematic itself is close but the location numbers are different. When you installed the 47µf/50v cap, it would have been likely seen as a short and either blew that resistor I referenced, it acts like a fuse for the standby ic.

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                    #29
                    Re: Samsung Syncmaster 245b BN44-00195A

                    Originally posted by R_J View Post
                    The schematic itself is close but the location numbers are different. When you installed the 47µf/50v cap, it would have been likely seen as a short and either blew that resistor I referenced, it acts like a fuse for the standby ic.
                    You are very clever. The resistor 44ohm was open. I replaced it with 43ohm, and now we're back. It wold have taken me ages to find the resistor fault. Have the S_B 5V. No voltage on +5 to the control board
                    The QB801S (QB802S on the schematic i guess) is B,C,E= 11V, 12V, 10.5V.
                    10.8 on ICP801S.
                    Last edited by Mandor; 04-07-2021, 12:45 PM.

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                      #30
                      Re: Samsung Syncmaster 245b BN44-00195A

                      I see what looks like a damaged trace off of one of the optocouplers, can you check this?
                      Attached Files

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                        #31
                        Re: Samsung Syncmaster 245b BN44-00195A

                        No, that's just some glow from the lamp. Continuity is good on that transformer pin and the trace from optocoupler going arround it.

                        Comment


                          #32
                          Re: Samsung Syncmaster 245b BN44-00195A

                          Originally posted by Mandor View Post
                          The QB801S (QB802S on the schematic i guess) is B,C,E= 11V, 12V, 10.5V.
                          10.8 on ICP801S.
                          Those voltages are low, The collector needs to be around +25 volts to be able to supply +18 volts on the emitter for the other ic's

                          I see that you have the power supply turned ON with a short between standby and PS_ON. Remove that short so the power supply is in standby and recheck the voltages on qb801S, It should be around +20 volts on the collector, and close to 0 on the base and emitter. This will check that the standby circuit is supplying a good +20v and it is not getting loaded down after the emitter.
                          Was RB808 (sch RB809) ever checked or replaced?
                          Last edited by R_J; 04-07-2021, 07:18 PM.

                          Comment


                            #33
                            Re: Samsung Syncmaster 245b BN44-00195A

                            Originally posted by budm View Post
                            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.
                            Looks like it arced across the top of the PCB, from QM802 to BM801 and what looks like a resistor, albeit I probably can't see all the stripes.
                            Last edited by RJARRRPCGP; 04-07-2021, 11:10 PM.
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                              #34
                              Re: Samsung Syncmaster 245b BN44-00195A

                              Originally posted by R_J View Post
                              Those voltages are low, The collector needs to be around +25 volts to be able to supply +18 volts on the emitter for the other ic's

                              I see that you have the power supply turned ON with a short between standby and PS_ON. Remove that short so the power supply is in standby and recheck the voltages on qb801S, It should be around +20 volts on the collector, and close to 0 on the base and emitter. This will check that the standby circuit is supplying a good +20v and it is not getting loaded down after the emitter.
                              Was RB808 (sch RB809) ever checked or replaced?
                              18.3V on collector. 0 on base and emitter on standby.
                              Rb808 measures 2.1 ohm in circuit. Colors say 2ohm.

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                                #35
                                Re: Samsung Syncmaster 245b BN44-00195A

                                That 18v is still a bit low but might be ok. Check the voltage across the main filter CP801S and see if the voltage goes up when you power ON the power supply (S_B~PSON) it should increase from 317v to around 385v. If it does, the pfc circuit is working, if it does not, then the pfc circuit is not working.
                                When the power supply is turned ON qb801-E supplies the pfc ic pin 8 as well as ICM801 pin15. ICM801 (MC33067P) requires a min vcc of 9v to start and should have a supply of 16 volts, so that is why you will not get any of the other secondary voltages.
                                Last edited by R_J; 04-08-2021, 10:04 AM.

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                                  #36
                                  Re: Samsung Syncmaster 245b BN44-00195A

                                  CP801S is always 310-315V. No change on power on.

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                                    #37
                                    Re: Samsung Syncmaster 245b BN44-00195A

                                    Originally posted by Mandor View Post
                                    CP801S is always 310-315V. No change on power on.
                                    Well the pfc circuit is not working. There is a small jumper wire, J808 which supplies vcc to icm801, If you lift one end of that jumper wire, then power on the board and see if the pfc voltage comes up to 385v. By doing this it will eliminate icm801 loading down the vcc line and preventing the pfc from operating. The PFC ic requires 12.5 volts to start up, it is only getting 10.5 according to your post#29

                                    I suspect you may still have a problem with the standby circuit, not operating properly and not supplying enough raw vcc voltage. It could be that the optocoupler was damaged or one of the zener diodes around the ic
                                    Last edited by R_J; 04-08-2021, 10:37 AM.

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                                      #38
                                      Re: Samsung Syncmaster 245b BN44-00195A

                                      J808 is next to icb801s. Disconnecting it raises vcc on icp801s to 15v.
                                      I desoldered the pin 15 of icm801 and no change. Main cap at 315v.
                                      I have desoldered all the optocouplers before and tested with multimeters ok.
                                      Zenner arround which ic? Zdb801 is 14.9v across terminals when ps on.
                                      Qb801 Bce 15.5, 17, 15v.

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                                        #39
                                        Re: Samsung Syncmaster 245b BN44-00195A

                                        If the pfc ic is getting 15v for it's vcc it should be working, but it is not, so something must be wrong in that circuit. There is a low ohm resistor on the source of QP801S (pfc fet) check if it is ok and not open. Then check that DP803 is not bad as well.
                                        Last edited by R_J; 04-08-2021, 08:14 PM.

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                                          #40
                                          Re: Samsung Syncmaster 245b BN44-00195A

                                          RP819, the 5W resistor on QP801S source mesures 0.21 ohm. Has 0.15ohm declared on it and is marked as RP814S on the board.
                                          The diode DP803 was 0.2V both ways in the circuit so I desoldered it and it tested 0.5V ok, so good. But DP803 on the board is connected to pin 7 of ICP801S. If you are referring to the DP803 on the schematic, between pin4 of ICP801S and ground, I can't find it. There is the SMD capacitor CP806 there, but I dont' see the diode.

                                          The PFC are P-marked components arround ICP801S?
                                          Should I keep the jumper J808 open? I soldered Pin 15 of ICM801 back.

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