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Samsung BN44-00505A(PD23A0Q) psu, smd transistor types

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    #41
    Re: Samsung BN44-00505A(PD23A0Q) psu, smd transistor types

    Hi, I see there are different problems detailed here:

    a) for symptoms such as: CM 804 blown up... NO POWER AT ALL (usual in LG or SAMSUNG PSUs !), I got a nice kit for a Samsung PSU BN44-00505A PD23A0Q Rev 1.3 2012.03.14, TV Model code : LT24B301EW/EN, (w3.ebay.fr/itm/234943555865 e.g. about 5$) which works fine: you SHOULD change ALL the following at the SAME time in order to avoid same problems again :
    * integrated STRW6052S (STRW6053S)
    * caps condensateur ceramique 221pF 1KV
    * diodes bridge GBU8K KBU8K = KBU606
    * fuse 3.15 A 250V AC
    * check resistance RM803 / I changed for 2W 39silver 5%, (doesn't matter if OK)
    the kit worked perfectly fine. (see funny repair such as w3.youtube.com/watch?v=iDpRCC6Xt8s)

    b) for symptoms such as: CM855, 1200 μf 10v 105°c blown up (rounded top=blown up!) : for example Power is there, remote control if flashing, but NO image at all... change itCM855 , check the 4 big diodes DM852 to DM859.
    regards P-M K.

    Comment

      #42
      Hi everyone,
      I just repaired one of these power supplies, classic breakdown of str6052s and cm804 (snubber cap).
      Now all the power supplies are OK but I have strange behavior on the TV, once I turned it off using the remote control it never turned back on even though the power supply is still OK. I did several tests and came to the conclusion that by disconnecting the PS_ON conductor, the TV turns on and off correctly. Strange! The PS_ON signal coming from the main board emits a 5V signal for a few seconds when turned on and then returns to 0V (if disconnected from the power supply) while if I connect it to the power supply board it always remains at 0V. Question 1: How does the TV turn on and off properly without connecting this wire? Question 2: Does anyone have the wiring diagram of the secondary part or can tell me which source of the fault? I tried to follow the circuit of the power supply to understand where this signal acts but without an electrical diagram it is difficult. I found the two suspicious QM853 and QM855 but from the measurements made they could be MOSFETs since I measure a channel diode between source and drain. They are signed 2P but it is difficult to say that they are bipolar. The other components also seem OK to me but without the diagram I struggle.

      Thank you all.

      Comment

        #43
        Originally posted by username_is_angelo View Post
        Hi everyone,
        I just repaired one of these power supplies, classic breakdown of str6052s and cm804 (snubber cap).
        Now all the power supplies are OK but I have strange behavior on the TV, once I turned it off using the remote control it never turned back on even though the power supply is still OK. I did several tests and came to the conclusion that by disconnecting the PS_ON conductor, the TV turns on and off correctly. Strange! The PS_ON signal coming from the main board emits a 5V signal for a few seconds when turned on and then returns to 0V (if disconnected from the power supply) while if I connect it to the power supply board it always remains at 0V. Question 1: How does the TV turn on and off properly without connecting this wire? Question 2: Does anyone have the wiring diagram of the secondary part or can tell me which source of the fault? I tried to follow the circuit of the power supply to understand where this signal acts but without an electrical diagram it is difficult. I found the two suspicious QM853 and QM855 but from the measurements made they could be MOSFETs since I measure a channel diode between source and drain. They are signed 2P but it is difficult to say that they are bipolar. The other components also seem OK to me but without the diagram I struggle.

        Thank you all.
        So do the backlights turn off as well with the remote with that wire out? did you try the on off button on the tv when you were testing it or just the remote, just to make sure it's not a remote or ir board issue.
        Last edited by nomoresonys; 01-10-2024, 09:31 AM.

        Comment

        • username_is_angelo
          #43.1
          username_is_angelo commented
          01-10-2024, 02:43 PM
          Editing a comment
          This is the situation:
          With ps_on connected:
          This signal (PS_ON) does not move and remains at 0V both by operating the remote control TV and from the key.
          Tensions on the exit of the Switching power supply are present and stable while on the connector there is only A5V, but not present B5V and not even Vamp and B13V.

          If you disconnect PS_ON, operating from remote control or button, the tensions on the connector are correct and the backlight lights up and turns off correctly. A correction compared to what has been said before: With PS_ON disconnected, the 5V voltage on this signal is present for the entire duration of the TV.

          I don't explain how it is possible.
        #44
        Ok, I got the ps-on and the bl-on confused, I don't know, wonder if it's one of those always on powerboards?

        Comment

          #45
          The BLU_ON signal rises to 5V when the TV is on and drops to GND when it is off. So is that the signal that controls the power supplies? I was convinced it was PS_ON....
          I'd like to understand what PS_ON is for and find the fault that leads to the behavior I described. I don't think I can trust myself to leave it unplugged...

          Comment

            #46
            PS-on signal does come from mainboard to turn the powerboard and tv fully on, BLU-ON is for backlight on and is suppose to change voltage when you turn on tv as PS-ON should too.

            Comment

              #47
              Ok so the BL turns on the backlight while PS-ON turns on the auxiliary power supplies. Following the circuit it seems to have understood that the two transistors QM853 and QM855 OR the presence of the two signals: presence of backlight voltage and PS_ON. Maybe that's why the TV still works even without PS_ON connected. I would like to understand why the PS_ON signal is knocked down to GND when connected. The fault could fall on the two transistors but I can't figure out what type of components they are. By measuring them they would seem like MOS but even in this case the behavior is very strange.

              Comment

                #48
                Originally posted by roberto77 View Post
                Re: Samsung BN44-00505A(PD23A0Q) psu, smd transistor types

                FYI, replaced CM855 with a new 10 V 1200 uF, TV works again.
                +1

                replaced CM855 with 1500uF 16V cap and the screen finally turned on

                Comment

                  #49
                  CAN SOMEONE HELP ME? WHAT IS THE REFERENCE OF THE DM801 DIODE?

                  Comment

                    #50
                    Originally posted by ferfer View Post
                    CAN SOMEONE HELP ME? WHAT IS THE REFERENCE OF THE DM801 DIODE?
                    DM801 - UF4007
                    Attached Files

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