Announcement

Collapse
No announcement yet.

Samsung 242mp PSU problem

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Samsung 242mp PSU problem

    Samsung Syncmaster 242mp
    PSU model: PN120LPS-VF rev 2.0
    Code: BN96-01849A

    Mainb model: P024FS
    Code: BN41-00552C


    Description of problem/defect:
    Monitor works fine at all inputs if leaved unplugged for 2hrs+, until power off. It will not power up again unless it has been unplugged for those 2hrs.

    What i have done/measured:
    Changed a bunch of caps (bottom leakage). Reheated/solder entire PSU. All this whitout any positive effect.

    Measured at full function:
    392v at big 450v/150uf cap
    24v to inverter
    12v and 5v to main
    all ok

    Measured when refusing to power up:
    306v at big cap
    18v to inverters, slowly dropping to zero!
    12v mainb feed measures zero
    5v mainb feed is fine.

    I have not been able to find any schematics for the PSU. I have very little knowledge of how such PSUs work.

    Supplied form wall is 240v/50hz.
    Attached Files

    #2
    Re: Samsung 242mp PSU problem

    Hi I have been unable to upload the Pdf but the manual is here


    Its very impressive and lots of tests.

    Can you post a picture of the underside of the board
    Voltage at the Big Cap is too low when not working - did you change that?
    Whilst it fails less often than smaller caps it is between 2 heatsinks so may be
    "cooked" What make is it?
    Last edited by selldoor; 01-31-2012, 02:48 PM.
    Please upload pictures using attachment function when ask for help on the repair
    http://www.badcaps.net/forum/showthread.php?t=39740

    Comment


      #3
      Re: Samsung 242mp PSU problem

      Ok, thanks! Checked it out. But there is not really anything about the PSU board there. those steps just end up as "check adapter" (psu) and that is just my problem.... little unsure where to start, since the psu is so compact its even harder without schematic.

      Comment


        #4
        Re: Samsung 242mp PSU problem

        Originally posted by selldoor View Post
        Can you post a picture of the underside of the board
        Voltage at the Big Cap is too low when not working - did you change that?
        Whilst it fails less often than smaller caps it is between 2 heatsinks so may be
        "cooked" What make is it?
        Yes i can fix a underside pic tomorrow. Actually i changed the 450/150uf with one taken from a samsung 32" as it is a little stupid place to put a cap on, lots of heat there.... But same readings with both caps so there is something else messing it up. don´t know what make it is as typing, check tomorrow.

        Comment


          #5
          Re: Samsung 242mp PSU problem

          Some joints look "cold" but i belive it is the original "solder wire" charactheristics, they have been reheated by me.
          Attached Files

          Comment


            #6
            Re: Samsung 242mp PSU problem

            Hi,
            this is my first post here..
            I'm following this thread with high interest.
            I too have a broken Samsung 242MP power supply (PN120LPS-VF).
            The TV/Monitor won't switch on anymore, no stdby led, nothing....

            My symptoms on the PSU are: No 12V main, no 5V main, no 24V, no 5V STDBY.
            Voltage at BIG Cap: 380V (w/ 230V 50Hz mains).
            I've replaced several smaller cap's (not all) with new, good quality Low ESR ones, but none of the original caps seemed really "bad" (all of them measured capacity's within the specs). No signs of leakage or bulged.

            The absence of even the 5V stdby voltage, makes me think it must be one of the SMPS management IC's or the power FETs, but I also don't have a schematic diagram, which would be really useful for further diagnosing. Right now I have no clue where to look.

            @Jont3: Your too low voltage at the Big cap 450V, makes me suspect the bridge rectifier. maybe one of the diodes have gone open-circuit. There's not much else between the Mains and the big cap except the diode bridge and some noise filtering coils.

            Ed pe9ghz
            Last edited by pe9ghz; 01-31-2012, 05:22 PM.

            Comment


              #7
              Re: Samsung 242mp PSU problem

              Originally posted by Jont3 View Post
              What i have done/measured:
              Changed a bunch of caps (bottom leakage).
              Where did you buy those Suncon caps with the "X" vent? If ebay, there is a good chance they are counterfeit/fake which might be part of the problem.

              The Sanyo/Suncon caps should have a "K" vent like the smaller caps by the black/red connectors in your first photo.
              Last edited by retiredcaps; 01-31-2012, 07:16 PM.
              --- begin sig file ---

              If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

              We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

              Please do not post inline and offsite as they slow down the loading of pages.

              --- end sig file ---

              Comment


                #8
                Re: Samsung 242mp PSU problem

                Originally posted by pe9ghz View Post
                The absence of even the 5V stdby voltage, makes me think it must be one of the SMPS management IC's or the power FETs, but I also don't have a schematic diagram, which would be really useful for further diagnosing. Right now I have no clue where to look.
                Start by looking at the multipin ICs (like 8 pin) and looking for its datasheet. Once you find the correct datasheet, they might have a "typical" application circuit diagram that shows an example schematic.

                For example, looking at the pictures, it might be IC604S on the backside because it is close to the AC plug. What is the part number of that IC?
                --- begin sig file ---

                If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                Please do not post inline and offsite as they slow down the loading of pages.

                --- end sig file ---

                Comment


                  #9
                  Re: Samsung 242mp PSU problem

                  Originally posted by pe9ghz View Post

                  @Jont3: Your too low voltage at the Big cap 450V, makes me suspect the bridge rectifier. maybe one of the diodes have gone open-circuit. There's not much else between the Mains and the big cap except the diode bridge and some noise filtering coils.

                  Ed pe9ghz
                  Ok, but wouldn´t that cause a more permanent problem? as it actually works if left unplugged for a while.... will check anyhow.




                  Originally posted by retiredcaps View Post
                  Where did you buy those Suncon caps with the "X" vent? If ebay, there is a good chance they are counterfeit/fake which might be part of the problem.

                  The Sanyo/Suncon caps should have a "K" vent like the smaller caps by the black/red connectors in your first photo.
                  Bought the caps from www.elfa.se, so i really hope that they are originals. Hopefully i will be able to post better/bigger photos tonight ala macro.

                  Comment


                    #10
                    Re: Samsung 242mp PSU problem

                    Originally posted by Jont3 View Post
                    Ok, but wouldn´t that cause a more permanent problem? as it actually works if left unplugged for a while.... will check anyhow.
                    240 AC x 1.414 (rectified) = 339V DC. Since you are getting 392V DC when the lcd is working, I believe this implies that there is some PFC involved. I seem to recall reading that Europe had some sort of law that all electronics had to have some sort of PFC?

                    You can measure the DC voltage directly at the bridge rectifier pins when the lcd is working and not working and then do a comparison. Be careful as all this stuff is high voltage since you are on the hot side.

                    Bought the caps from www.elfa.se, so i really hope that they are originals.
                    I'm not familiar with that distributor. If it is a well known big company, then the caps are probably good. I just haven't seen them with the X vent, only the K vent. There are a lot of fakes on ebay.
                    --- begin sig file ---

                    If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                    We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                    Please do not post inline and offsite as they slow down the loading of pages.

                    --- end sig file ---

                    Comment


                      #11
                      Re: Samsung 242mp PSU problem

                      Originally posted by retiredcaps View Post
                      Start by looking at the multipin ICs (like 8 pin) and looking for its datasheet. Once you find the correct datasheet, they might have a "typical" application circuit diagram that shows an example schematic.

                      For example, looking at the pictures, it might be IC604S on the backside because it is close to the AC plug. What is the part number of that IC?
                      Thanks,
                      IC804S (hard to read from the pictures) has a marking 230D6 (SOIC8).
                      Some others:
                      IC801S = ST L6561D SO-8 Power Factor Corrector PDF
                      I'll study the application note and try to compare it with the actual PSU board.

                      IC802S = DM0365 (probably FSDM0365RN - Green Mode Fairchild Power Switch) DIP8.
                      This could be the regulator for the stdby_5V.

                      Comment


                        #12
                        Re: Samsung 242mp PSU problem

                        Originally posted by pe9ghz View Post
                        IC804S (hard to read from the pictures) has a marking 230D6 (SOIC8).
                        .
                        Probably attached?
                        Attached Files
                        Please upload pictures using attachment function when ask for help on the repair
                        http://www.badcaps.net/forum/showthread.php?t=39740

                        Comment


                          #13
                          Re: Samsung 242mp PSU problem

                          Originally posted by retiredcaps View Post
                          240 AC x 1.414 (rectified) = 339V DC. Since you are getting 392V DC when the lcd is working, I believe this implies that there is some PFC involved. I seem to recall reading that Europe had some sort of law that all electronics had to have some sort of PFC?

                          You can measure the DC voltage directly at the bridge rectifier pins when the lcd is working and not working and then do a comparison. Be careful as all this stuff is high voltage since you are on the hot side.



                          I'm not familiar with that distributor. If it is a well known big company, then the caps are probably good. I just haven't seen them with the X vent, only the K vent. There are a lot of fakes on ebay.
                          Everything here has PFC.... probably law for new products.
                          Elfa is a big company, would be safe then.

                          Done some measuring on the bridge rectifier as follows:
                          100% function:
                          with lcd on connected to computer via dvi 244V
                          in standby mode 311V

                          No function:
                          309V

                          This time it was even more random plugged it in and out for about 7 times before it died, 8th time dead... 9th time 100% functional, 10th time dead, 10minutes later 100% functional.
                          Also noticed a component RP839 (see pictures), doesn´t it look a little to black? from heat maybe? I just stick to the cold/secondary side of electronics, this hot/primary side PFCed stuff is not my area. Right now i´am lost.....
                          Attached Files
                          Last edited by Jont3; 02-01-2012, 02:18 PM.

                          Comment


                            #14
                            Re: Samsung 242mp PSU problem

                            Originally posted by Jont3 View Post
                            .....
                            Also noticed a component RP839 (see pictures), doesn´t it look a little to black? from heat maybe? I just stick to the cold/secondary side of electronics, this hot/primary side PFCed stuff is not my area. Right now i´am lost.....
                            Your RP839 looks the same as on mine.. Black body power resistor. It has a (faint) marking: 8.4Ohm, maybe.

                            Comment


                              #15
                              Re: Samsung 242mp PSU problem

                              Originally posted by selldoor View Post
                              Probably attached?
                              Thanks! that must be the right datasheet NCP1230

                              Comment


                                #16
                                Re: Samsung 242mp PSU problem

                                Originally posted by Jont3 View Post
                                in standby mode 311V

                                No function:
                                309V
                                Since your bridge rectifier is 311V DC when standby and 309V when not, the 2V DC difference is not significant. So I believe your rectifier is okay. 311DC /1.414 = 219.9V AC.

                                When the lcd is on, the PFC should be around 392V DC as you first reported back in post #1.

                                Refer to datasheet found be selldoor.

                                On NCP1230, it looks like pin 1, PFC_Vcc, controls the PFC chip. Figure 29 shows how everything is connection in a typical application. If everything is working correctly, pin 1 connects to pin 6 (VCC) and provides bias to the PFC controller. In standby mode, the PFC_Vcc is not active. PFC_Vcc is also shutdown when a fault condition is found.

                                Pin 6 is enabled when the voltage is between 11.6 and 13.6 with typical being 12.6V. The startup capacitor is recommended to be at least 47uF according to the paragraph just under Figure 38.

                                There are many possibilities, but I'll just point out some that I would check first.

                                1) Check the startup cap. If it has not been replaced and you have a quality cap, it is easy to change out. These little caps can be bad without bloating. This cap may be 47uF 50V and is nearby NCP1230.

                                This is also a good time to mention that if some caps were visibly bulged, most here would recommend that you replace all the caps unless you have an ESR meter to check the uF and ESR of originals.

                                2) When the lcd doesn't work, check the DC voltage across the startup cap. It should be at least 11.6V DC and steady.

                                3) If the startup cap is good, then check NCP1230 pin 6 (pin 4 is your GND). It should be around 12.6V and steady. If it is not 12.6V, there are a couple of components in figure 29 that could be at fault like a diode. Or the NCP1230 chip itself could be bad.

                                4) If pin 6 is at 12.6V, then check pin 1 (pin 4 GND again) and see if it is working and sending the info to the PFC chip.

                                PS. Great clear focused photos. It took 3 tries, but this is by far the best because I can read everything clearly.
                                Last edited by retiredcaps; 02-02-2012, 12:18 AM.
                                --- begin sig file ---

                                If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                                We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                                Please do not post inline and offsite as they slow down the loading of pages.

                                --- end sig file ---

                                Comment


                                  #17
                                  Re: Samsung 242mp PSU problem

                                  1) Check the startup cap. If it has not been replaced and you have a quality cap, it is easy to change out. These little caps can be bad without bloating. This cap may be 47uF 50V and is nearby NCP1230.

                                  This is also a good time to mention that if some caps were visibly bulged, most here would recommend that you replace all the caps unless you have an ESR meter to check the uF and ESR of originals.
                                  Will check NCP1230 circuit and cap, i did change all caps totally 17 new and a fresher big one. All suncon except for one elna low esr 10uf/50V i really do not think caps are the problem anymore. Thanks for your kind words and Help so far https://www1.elfa.se/data1/wwwroot/a...s/06719173.pdf
                                  Last edited by Jont3; 02-02-2012, 01:49 AM.

                                  Comment


                                    #18
                                    Re: Samsung 242mp PSU problem

                                    Originally posted by retiredcaps View Post
                                    Since your bridge rectifier is 311V DC when standby and 309V when not, the 2V DC difference is not significant. So I believe your rectifier is okay. 311DC /1.414 = 219.9V AC.

                                    When the lcd is on, the PFC should be around 392V DC as you first reported back in post #1.

                                    Refer to datasheet found be selldoor.

                                    On NCP1230, it looks like pin 1, PFC_Vcc, controls the PFC chip. Figure 29 shows how everything is connection in a typical application. If everything is working correctly, pin 1 connects to pin 6 (VCC) and provides bias to the PFC controller. In standby mode, the PFC_Vcc is not active. PFC_Vcc is also shutdown when a fault condition is found.

                                    Pin 6 is enabled when the voltage is between 11.6 and 13.6 with typical being 12.6V. The startup capacitor is recommended to be at least 47uF according to the paragraph just under Figure 38.

                                    There are many possibilities, but I'll just point out some that I would check first.

                                    1) Check the startup cap. If it has not been replaced and you have a quality cap, it is easy to change out. These little caps can be bad without bloating. This cap may be 47uF 50V and is nearby NCP1230.

                                    This is also a good time to mention that if some caps were visibly bulged, most here would recommend that you replace all the caps unless you have an ESR meter to check the uF and ESR of originals.

                                    2) When the lcd doesn't work, check the DC voltage across the startup cap. It should be at least 11.6V DC and steady.

                                    3) If the startup cap is good, then check NCP1230 pin 6 (pin 4 is your GND). It should be around 12.6V and steady. If it is not 12.6V, there are a couple of components in figure 29 that could be at fault like a diode. Or the NCP1230 chip itself could be bad.

                                    4) If pin 6 is at 12.6V, then check pin 1 (pin 4 GND again) and see if it is working and sending the info to the PFC chip.

                                    PS. Great clear focused photos. It took 3 tries, but this is by far the best because I can read everything clearly.
                                    Checked startup cap, would be the new 10uf/50V reading steady 14.5V at function of display. Also checked voltage at all four optocouplers reading 1.3Vx4 (on led side that is) thinking if they are not "on" there will not be any voltage at NCP1230 either. pulled the cord before checking pin6 witch was a little mistake, 14.5V seems as too much here.

                                    Anyways at non fuction i read zero at startup cap, three of the optocouplers are zero and one 4V (PC102S) may be of less importance but i still did this so. Popped up one side of all diodes i could find on enitre board and DMMed them, thats about as far i got tonight.... little unsure on the heatsinked ones some schotty i belive, but all small are ok. still got the 5V output and 1V on the 13V output this time, and a 16-18V on 24V output dropping.

                                    From what i experinced it actually withstands multiple "cord pulls" at a higher amount laying upside-down than mounted in chassis, like a bad solder-joint feeling..... it´s getting to me now... :P

                                    can this be another chip? 230A6 not D... just thinking about the 14.5V´s
                                    Last edited by Jont3; 02-02-2012, 05:27 PM.

                                    Comment


                                      #19
                                      Re: Samsung 242mp PSU problem

                                      1) Okay, let's start even more basic. When the lcd is not working, pin 8 is your high voltage startup pin. It should be around 310V DC. Measure pin 8. Pin 4 is GND.

                                      2) Is there a 47uF 50V cap on the board? 10uF is too low for a startup cap according to the datasheet (again paragraph under figure 38).

                                      3) We need to know the DC voltage of pin 6.

                                      4) Other suggestions. When board is not working and after you take all the measurements (pins 1, 6, 8), get a wooden stick and gently press down on some of the board to see if there are any bad solder joints. I know you said you reheated/resoldered the entire board, but just gently press down with a wooden stick.
                                      --- begin sig file ---

                                      If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                                      We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                                      Please do not post inline and offsite as they slow down the loading of pages.

                                      --- end sig file ---

                                      Comment


                                        #20
                                        Re: Samsung 242mp PSU problem

                                        Originally posted by retiredcaps View Post
                                        1) Okay, let's start even more basic. When the lcd is not working, pin 8 is your high voltage startup pin. It should be around 310V DC. Measure pin 8. Pin 4 is GND.

                                        2) Is there a 47uF 50V cap on the board? 10uF is too low for a startup cap according to the datasheet (again paragraph under figure 38).

                                        3) We need to know the DC voltage of pin 6.

                                        4) Other suggestions. When board is not working and after you take all the measurements (pins 1, 6, 8), get a wooden stick and gently press down on some of the board to see if there are any bad solder joints. I know you said you reheated/resoldered the entire board, but just gently press down with a wooden stick.
                                        Not working:
                                        8-4 0V, 6-4 0V, 1-4 0V

                                        Working:
                                        8-4 0V, 6-4 14,5V, 1-4 14,5V

                                        It seems like pin 1 and 8 is not connected anywhere on the board, can it be another config than the one in figure 29? cap closest to pin 6 is 10uf/50V there is also a 22uf/50V neaby but it is not to be called starting cap, both with the same steady 14.5V (CP822 & CP826) i even checked the old caps for values, and this is the original vaules nothing beyond 22uf/50V is on the board. Also tried the wooden stick with no luck.

                                        http://www.onsemi.com/pub_link/Colla...NCP1230A-D.PDF
                                        Last edited by Jont3; 02-03-2012, 02:14 PM. Reason: Datasheet

                                        Comment

                                        Working...
                                        X