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    #1

    Samsung LCD Power Board turning on and off.

    I have a Samsung LCD that has a Dong Yang MK32P5B series Q power board that is having issues. Sometimes the TV comes on, sometimes not....very sporatic. Main filter cap looks good at 172.2 VDC, but nothing on the rail. Samsung recapped this with Panasonic EB's and FM's for free under their capacitor program, but it was having problems before that (which is why I had them do the recap). I thought that this might have solved my problem, but it has not. I have posted pics below....can someone give me some insight as to where I can run through critical voltage points and troubleshoot this board? Thanks in advance!!
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    #2
    Re: Samsung LCD Power Board turning on and off.

    Originally posted by waitery View Post
    can someone give me some insight as to where I can run through critical voltage points and troubleshoot this board?
    On the bottom right is connector. List each connector, its legend, and DC voltage.

    Maybe one says 5V SB?

    edit: There is also a connector at the top. Do the same.
    Last edited by retiredcaps; 10-01-2011, 11:02 PM.
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      #3
      Re: Samsung LCD Power Board turning on and off.

      1) If they replaced the caps, check the soldering work for cold joints with a 10x magnifying glass. Maybe the tech who did it isn't all that great at soldering?

      2) What are those light green caps? Who makes them and what series are they?
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        #4
        Re: Samsung LCD Power Board turning on and off.

        And PlainBill discusses in general how TVs work with the 5V SB and main board at (just 30 minutes ago)

        https://www.badcaps.net/forum/showpo...6&postcount=17
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          #5
          Re: Samsung LCD Power Board turning on and off.

          This is the 24 volt rail. 14 pins in total, pins running top to bottom in this order:

          NC
          BL
          GRD
          GRD
          GRD
          GRD
          GRD
          24V
          24V
          24V
          24V
          24V

          I got .72 vdc coming out of these....it is connected to the main board and I am trying to fire up the LCD with the power button.

          Comment

            #6
            Re: Samsung LCD Power Board turning on and off.

            Originally posted by waitery View Post
            This is the 24 volt rail.
            I did an edit in post #2. Please also do the same for the top connector. We need to find where 5V SB is first. Then PS_ON.
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              #7
              Re: Samsung LCD Power Board turning on and off.

              Sorry, I thought that you might go there.....I should have just typed it out. Here is the way that the rail is comprised:

              Two lines of pins running side by side, 12 in each line, so 24 total. The lines are listed as follows:

              1-2 PS NC
              3-4 SB GND
              5-6 GND GND
              7-8 12.8V 12.8V
              9-10 GND GND
              11-12 GND GND
              13-14 5.3V 5.3V
              15-16 5.3V 5.3V
              17-18 GND GND
              19-20 12V-GND
              21-22 12V 12V
              23-24 NC NC

              Above that rail is another smaller rail, single line of 5 pins as follows:
              1 BLU
              2 ADIM
              3 PWM
              4 GND
              5 +5V

              I am showing .007 volts on all +5 and +5.3 lines, assumes everything is connected to the main board, power on and hitting the power button.
              Last edited by waitery; 10-01-2011, 11:32 PM.

              Comment

                #8
                Re: Samsung LCD Power Board turning on and off.

                Pin 3 is your standby. It needs to be 5V DC before the TV will turn on. If it is 0.007, then like your lcd, either the startup cap is bad, the smps controller, or something in the circuitry.

                I see a variety of vents on the caps which tells me that Samsung cheaped out and didn't replace all the caps with Panasonic. That green color is still unknown and I see UCC (brown). Please list all the caps manufacturers and brands. UCC KZG are bad caps and they fail without bloating. You see KZG in a few motherboards.
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                  #9
                  Re: Samsung LCD Power Board turning on and off.

                  OK, pin 3 reads good at 5.10 and it is steady...we are good there. Here are the brands that I am seeing:

                  Green ones are Lelon and the other smaller brown ones are Samwha. To your point, there are a few that the tech didn't swap out and they are KMG brand.

                  How should I proceed?

                  Comment

                    #10
                    Re: Samsung LCD Power Board turning on and off.

                    Originally posted by waitery View Post
                    OK, pin 3 reads good at 5.10 and it is steady...we are good there.

                    How should I proceed?
                    On pin 1 (PS), re-read post #4 and what PlainBill says. So measure pin1. If you have min/max on your dmm, this is a good time to use it.
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                      #11
                      Re: Samsung LCD Power Board turning on and off.

                      Originally posted by waitery View Post
                      Green ones are Lelon and the other smaller brown ones are Samwha. To your point, there are a few that the tech didn't swap out and they are KMG brand.
                      Members will probably chime in and recommend that you replace all the above with Panasonic FM. One or more of those caps could have high ESR which explains why the tv is flakey in turning on. As the set warms up, the cap ESR drops.
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                        #12
                        Re: Samsung LCD Power Board turning on and off.

                        OK, read his post and here is what I get from Pin #1:

                        .35 volts, then I hit the power button and we're at 3.7 volts. I kept hitting the power button, the voltage hits 3.7, then goes back down to .35. It's there, it's just not starting it up.

                        Comment

                          #13
                          Re: Samsung LCD Power Board turning on and off.

                          Ahh, Fiddlesticks!!! This appears to be a variation of the BN44-00195A. Currently I am chasing problems (same general problem) on a BN44-00195A, and it's slow going. Please confirm a few points:

                          This is model number BN44-00214A

                          The 16 pin IC is MC34067P

                          A few points - a number of the BN44-00214A are available on eBay.

                          Someone in Great Britain has a repair kit for this power supply.

                          I have been unable to find a schematic for the other version; I wounder if this one will be easier.

                          EDIT: Yes!!! I found the schematic on Elektrotanya. And Ohm Supplies Ltd lists the parts in their repair kit.

                          PlainBill
                          Last edited by PlainBill; 10-02-2011, 05:54 AM.
                          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

                            #14
                            Re: Samsung LCD Power Board turning on and off.

                            Hi PlainBill-

                            Yes, BN44-00214A is the board designation.

                            The 16 pin IC is listed as MC33067P, so it is really close to what you listed.

                            Are you thinking that we can use the schematic to get the part numbers listed in the repair kit advertisment? Let me know what you think....

                            Comment

                              #15
                              Re: Samsung LCD Power Board turning on and off.

                              Originally posted by waitery View Post
                              Hi PlainBill-

                              Yes, BN44-00214A is the board designation.

                              The 16 pin IC is listed as MC33067P, so it is really close to what you listed.

                              Are you thinking that we can use the schematic to get the part numbers listed in the repair kit advertisment? Let me know what you think....
                              I think we haven't yet confirmed this is the same problem. The kit includes the input fuse, clearly that is not the problem in your case.

                              I also think I will be spending the next 6 hours of so watching football.

                              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

                                #16
                                Re: Samsung LCD Power Board turning on and off.

                                I replaced all of the startup caps with new 105 degree Panasonic caps. Still having the same issue. One thing I did notice when I got it fired up once is that the standby voltage on the #1 pin shot up to 3.95vdc. Usually it will just go up from .35 to 3.7 and do nothing. Not sure what would drive it up higher, but the higher voltage is making it start up. Still very inconsistent and when it wants to start up.

                                As I am taking some test mesurements on some of the components, I come across a diode (D8801) in the primary side. The anode side is violently changing from 95vdc to 108vdc to 121 vdc, fluctuating rapidly and then beleive it or not, it flips to VAC (yes that is VAC) for a second then back again to do the same thing 95/108/121vdc. I could not belive what my Fluke was telling me. Tried it again and same thing, it was switching over to VAC and the voltage range was all over the place. The cathode side is much more stable, but flipping every few seconds from 192vdc to 199 vdc and back again.....no VAC though.

                                As I was sitting here typing this out, my set just came on by itself....I didn't even push the power button....very frustrating!!

                                Any thoughts on how I can chase this down or a good starting place? Thanks guys!
                                Last edited by waitery; 10-02-2011, 04:22 PM.

                                Comment

                                  #17
                                  Re: Samsung LCD Power Board turning on and off.

                                  The diode in question is DB801. It's on the drive to the primary SMPS controller. It's probably a bad idea to put a DMM on that point - there are some very high voltage pulses on it.

                                  It's fairly easy to localize the area of the problem. I would prefer you download the schematic; it will make following along a lot easier. I'm going to use grid locators.

                                  On page 1, location B8 is the ON/OFF input. When it is high, QB851 (1-B7) begins to conduct, and current flows through the LED of PC802S (1-B7). This causes the phototransistor of PC802S (1-B7) to conduct. This pulls the base of QB802 (1-B6) high. Since QB802 (1-B6) is in an emitter follower configuration, the emitter also goes high, which provides power to the main SMPS controller.

                                  Troubleshoot by measuring the voltages from under the following conditions: TV in Standby; TV switched ON, but not powering up; TV operating. You are interested in every point from the ON/Off input through PC802S. Suspect a bad solder joint.

                                  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

                                    #18
                                    Re: Samsung LCD Power Board turning on and off.

                                    OK guys, we're watching TV! Cold solder joint found on Fairchild Mosfet located at QB802, just a step passed PC802S. I just kept getting these huge voltage swings at PC802, so I started backtracking and when I got to the FET and I touched it with my Fluke probe to get a reading and it was just enough pressure to start the TV without me having to press the on/off switch.....so thrilled! The joint was super weak looking before reworking it and applying three new beads of solder.

                                    Looks like she is holding steady, voltages all look good and there seem to be no problems. It fires up perfectly every time I hit the remote and touch the set's power button. I am going to burn test it to make sure that we have the issue buttoned up.

                                    Retired and PlainBill, THANK YOU SO MUCH for your help, patience and most of all, YOUR TIME! I would love to sit down and troubleshoot with you guys one on one! I appreciate you both!!

                                    Comment

                                      #19
                                      Re: Samsung LCD Power Board turning on and off.

                                      Originally posted by waitery View Post
                                      I am going to burn test it to make sure that we have the issue buttoned up.
                                      The last suggestion is to replace the remaining non Panasonic caps so your TV set will last longer.

                                      Good job!
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                                        #20
                                        Re: Samsung LCD Power Board turning on and off.

                                        Which capacitors are replaced for switching in and out of standby

                                        Comment

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