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    #1

    Samsung HT-P38 DVD Home Theater System

    Im trying to fix this for a friend. The unit powers on, and a few seconds later displays "Protection" and shuts down. All the caps on the PS look good. I focused some attention on the audio amp board. If I remove the large black connector on the left, the unit remains on.

    The audio board has 3 TAS5152 amp IC's. Wondering if they are a common failure.

    Any help appreciated!
    Attached Files
    Tags: None
    #2
    Re: Samsung HT-P38 DVD Home Theater System

    For what it's worth, i've managed to find the service manual HERE.

    The datasheet for that square chip (PWM modulator) is HERE. I notice it has an "Overload" input pin - might be worth probing that one, for starters, during power-up. Or actually, scratch that, it's not connected to anything on the board, it seems.

    On pages 4-5 in the service manual, there seems to be a list of issues that trigger the "Protect" mode - run through those and see if any / which one of those is the culprit
    Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

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      #3
      Re: Samsung HT-P38 DVD Home Theater System

      Thanks for the S/M.. I think I found the problem. I was just about to order new AMP IC's but in the service manual, one of the reasons for going into protection is voltage not provided to gate driver.

      On each IC there are 4 and I noticed I was missing the 12v+ on Pin 19 of the left channel IC. Then I noticed the melted 10 ohm resistor right next to it.

      Hopefully it's just that and the IC's are good. Will let you know!
      Attached Files

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        #4
        Re: Samsung HT-P38 DVD Home Theater System

        There we go I / we hope to hear the good news of revival soon, then

        At least according to the TAS5152 datasheet, the chips *should* be fine:

        Powering Up
        The TAS5152 does not require a power-up sequence. The
        outputs of the H−bridges remain in a high-impedance state
        until the gate-drive supply voltage (GVDD_X) and VDD
        voltage are above the undervoltage protection (UVP)
        voltage threshold (see the Electrical Characteristics
        section of this data sheet). Although not specifically
        required, it is recommended to hold RESET_AB and
        RESET_CD in a low state while powering up the device.
        This allows an internal circuit to charge the external
        bootstrap capacitors by enabling a weak pulldown of the
        half-bridge output.

        ... But then again, it would be interesting to know how and why that resistor melted...
        Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

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          #5
          Re: Samsung HT-P38 DVD Home Theater System

          Well it looks like that IC next to resistor may be bad. When I replaced resistor the 12v was being loaded down to around 4v. Without that resistor in place the 12v is present on all other pins. Does that make sense?

          Comment

            #6
            Re: Samsung HT-P38 DVD Home Theater System

            I removed that IC and still had same loading issue, so I removed that cap next to the bad resistor and I think it was broken. Then the voltages came back up without it in circuit. So I think I will end up replacing the IC, cap and resistor and see what happens.

            Does it make sense that cap would fail too with whatever happened?

            Comment

              #7
              Re: Samsung HT-P38 DVD Home Theater System

              Originally posted by kevinm34232 View Post
              Does it make sense that cap would fail too with whatever happened?
              Does the cap you removed measure shorted on a multimeter?
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                #8
                Re: Samsung HT-P38 DVD Home Theater System

                It shows 56 ohms, it looks like part of the ceramic has cracked off. I haven't done much with finding and troubleshooting SMD components other than IC's.

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                  #9
                  Re: Samsung HT-P38 DVD Home Theater System

                  Originally posted by kevinm34232 View Post
                  It shows 56 ohms, it looks like part of the ceramic has cracked off.
                  56 ohms and a crack suggests it is dead. See document that budm provided.

                  https://www.badcaps.net/forum/showpo...9&postcount=13
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                    #10
                    Re: Samsung HT-P38 DVD Home Theater System

                    Thanks, I will try to find a new one..

                    I don't see any markings on these SMD caps, does polarity matter?

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                      #11
                      Re: Samsung HT-P38 DVD Home Theater System

                      Originally posted by kevinm34232 View Post
                      Thanks, I will try to find a new one..

                      I don't see any markings on these SMD caps, does polarity matter?
                      Momaka uses this method and it seems to work for him on several repairs.

                      https://www.badcaps.net/forum/showpo...69&postcount=8
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                        #12
                        Re: Samsung HT-P38 DVD Home Theater System

                        Luckly the the S/M has a parts list, it's a 1uf 16V. No problem finding it just wondering about the polarity..

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                          #13
                          Re: Samsung HT-P38 DVD Home Theater System

                          Originally posted by kevinm34232 View Post
                          Luckly the the S/M has a parts list, it's a 1uf 16V. No problem finding it just wondering about the polarity..
                          SMD ceramic caps have no polarity.

                          You can substitue an 1uF 16V aluminum electrolytic cap if you want. Obviously you will have to pay attention to the polarity. You can figure it out by measuring the pad on the pcb and seeing which one is ground like I did here

                          https://www.badcaps.net/forum/showpo...1&postcount=23

                          One year later, the monitor is still running fine (used about 4 hours daily).
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                            #14
                            Re: Samsung HT-P38 DVD Home Theater System

                            Any guess to what happened here, could the cap have caused the resistor failure? It seems like the IC was apparently OK, but I had to order a new one anyway because a leg broke off and it was probably safer to replace it at this point..

                            Also the big heat sink goes over this area had to order the SMD cap.

                            Comment

                              #15
                              Re: Samsung HT-P38 DVD Home Theater System

                              It may very well have.

                              12v / (56+10)ohms = ~182mA , while that 10ohm 1206 (0.25w) resistor would only hold up to about 160mA max.
                              Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

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                                #16
                                Re: Samsung HT-P38 DVD Home Theater System

                                Yes the capacitor probably caused the problem. MLCC capacitors, like this one, tend to go short circuit in almost every failure of the latter.
                                Muh-soggy-knee

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                                  #17
                                  Re: Samsung HT-P38 DVD Home Theater System

                                  Thanks, installed the new capacitor and the short went away...

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                                    #18
                                    Re: Samsung HT-P38 DVD Home Theater System

                                    Originally posted by kevinm34232 View Post
                                    Thanks, installed the new capacitor and the short went away...
                                    Congrats!
                                    Muh-soggy-knee

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                                      #19
                                      Re: Samsung HT-P38 DVD Home Theater System

                                      I had a hard time with soldering the components this time, it seems like it's intermitternt. Sometimes I can set my Hakko FX-888 to 610 degrees and put a little solder on the tip and plenty of flux on the board and just touch the pins and it will make a nice clean connection.

                                      This time and others it seemed like the tip wasnt hot enough and it winds up messy and it smeared the solder.

                                      I don't know if its the soldering iron temperature just not being consistent or something else..

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                                        #20
                                        Re: Samsung HT-P38 DVD Home Theater System

                                        Originally posted by kevinm34232 View Post
                                        I don't know if its the soldering iron temperature just not being consistent or something else..
                                        I generally use 350C on my FX-888 with a 1.6mm chisel tip. I use the brass wool to keep the tip clean and not the wet sponge.

                                        Make sure to keep the tip clean and tinned. CuriousInventor makes excellent soldering videos.

                                        http://www.youtube.com/watch?v=I_NU2ruzyc4

                                        http://www.youtube.com/watch?v=3NN7UGWYmBY
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