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Yamahaha RX-V679 DC PRT High

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    Yamahaha RX-V679 DC PRT High

    Hey all,

    I have a Yamaha RX-V679 that is entering protection mode after a few seconds of turning on. Shows "DC PRT 77H" error when I disable the auto protection.

    All speaker terminals read ~0.4 volts across, except for the surrounds, which read 0 volts for right and ~0.9 volts on the left, which increases until the receiver kicks off. I'm thinking this is my problem child.

    I took it apart and started testing the main output transistors, and didn't see anything blown open (I did this without desoldering, however I compared to nextdoor channel and all were very similar). The attached picture shows the transistors. Attached picture shows them.

    Question is, what is my next step for testing?

    Thank you for your help!

    Service manual is located here, too big to attach

    https://drive.google.com/file/d/1VtI...ew?usp=sharing
    Attached Files

    #2
    Re: Yamahaha RX-V679 DC PRT High

    most likely the differential transistors . is there no dc offset adjusters ?

    Comment


      #3
      Re: Yamahaha RX-V679 DC PRT High

      Which ones are those?

      Not that I am aware of, but frankly I'm not that knowledgeable on receiver electronics.

      Comment


        #4
        Re: Yamahaha RX-V679 DC PRT High

        have you got a schematic ?

        Comment


          #5
          Re: Yamahaha RX-V679 DC PRT High

          Update:

          I put things back together so I could reverify some voltages. I checked all the active speaker terminals for voltage again, and everything that's active is reading about 400 mV, with close to 0 on the non active channels. I had a speaker hooked up to one of them, and it sounded very distorted unless it was at a whisper like loudness.

          Comment


            #6
            Re: Yamahaha RX-V679 DC PRT High

            Originally posted by petehall347 View Post
            have you got a schematic ?
            Schematic should be in the service manual above, I can attach the main board pdf possibly?

            Comment


              #7
              Re: Yamahaha RX-V679 DC PRT High

              need to check the power supply first . if thats wrong it will never work properly

              Comment


                #8
                Re: Yamahaha RX-V679 DC PRT High

                Originally posted by petehall347 View Post
                need to check the power supply first . if thats wrong it will never work properly
                Should I just be checking voltages coming out of the power supply then?

                Comment


                  #9
                  Re: Yamahaha RX-V679 DC PRT High

                  yes check those first .

                  Comment


                    #10
                    Re: Yamahaha RX-V679 DC PRT High

                    Originally posted by petehall347 View Post
                    yes check those first .
                    Checked these voltages, all correct. (within 5% or so)
                    Attached Files

                    Comment


                      #11
                      Re: Yamahaha RX-V679 DC PRT High

                      look for the -12.4v rail .

                      Comment


                        #12
                        Re: Yamahaha RX-V679 DC PRT High

                        On the main board, correct?

                        Comment


                          #13
                          Re: Yamahaha RX-V679 DC PRT High

                          yes .if you look at the input to the amps on the schematic its there .

                          Comment


                            #14
                            Re: Yamahaha RX-V679 DC PRT High

                            also measure at for example Q1002 base .should be 0v ..i ask this because offsets are high when active . might be stray voltage getting in here .
                            i have a feeling the fault might be the input switching chips .
                            lets see those voltages first though before i get carried away too much .

                            Comment


                              #15
                              Re: Yamahaha RX-V679 DC PRT High

                              Reads at -12.2V

                              Comment


                                #16
                                Re: Yamahaha RX-V679 DC PRT High

                                Originally posted by petehall347 View Post
                                also measure at for example Q1002 base .should be 0v ..i ask this because offsets are high when active . might be stray voltage getting in here .
                                i have a feeling the fault might be the input switching chips .
                                lets see those voltages first though before i get carried away too much .
                                Q1002 is in a Y shape, from the bottom of main board

                                -0.45V 0V

                                56.58V

                                Comment


                                  #17
                                  Re: Yamahaha RX-V679 DC PRT High

                                  what does it measure when that channel inactive ? like not selected .

                                  Comment


                                    #18
                                    Re: Yamahaha RX-V679 DC PRT High

                                    Originally posted by peterwheat View Post
                                    Hey all,

                                    I have a Yamaha RX-V679 that is entering protection mode after a few seconds of turning on. Shows "DC PRT 77H" error when I disable the auto protection.

                                    All speaker terminals read ~0.4 volts across, except for the surrounds, which read 0 volts for right and ~0.9 volts on the left, which increases until the receiver kicks off. I'm thinking this is my problem child.

                                    I took it apart and started testing the main output transistors, and didn't see anything blown open (I did this without desoldering, however I compared to nextdoor channel and all were very similar). The attached picture shows the transistors. Attached picture shows them.

                                    Question is, what is my next step for testing?

                                    Thank you for your help!

                                    Service manual is located here, too big to attach

                                    https://drive.google.com/file/d/1VtI...ew?usp=sharing
                                    So the Surround Left is the only one that has output offset that goes too high after a while then the receiver goes into output high DC shut down?

                                    Is it Surround Left? Or is it Surround Back Left? I ask because you were asked to check Q1002 which is for Surround Back Left, not Surround Left. Please Clarify as to which Left channel is bad.

                                    Below is for Surround Left checking:
                                    Once it goes into shutdown,what DCV do you get on jumper J245 (close to Surround Left output inductor L6, see service manual PDF page 118)?
                                    Is it Positive or Negative Voltage reading with ref to GND?
                                    Attached Files
                                    Last edited by budm; 08-07-2020, 03:13 AM.
                                    Never stop learning
                                    Basic LCD TV and Monitor troubleshooting guides.
                                    http://www.badcaps.net/forum/showthr...956#post305956

                                    Voltage Regulator (LDO) testing:
                                    http://www.badcaps.net/forum/showthr...999#post300999

                                    Inverter testing using old CFL:
                                    http://www.badcaps.net/forum/showthr...er+testing+cfl

                                    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                    http://s807.photobucket.com/user/budm/library/

                                    TV Factory reset codes listing:
                                    http://www.badcaps.net/forum/showthread.php?t=24809

                                    Comment


                                      #19
                                      Re: Yamahaha RX-V679 DC PRT High

                                      i only used Q1002 as an example .. its fairly straightforward looking at the schematic .
                                      from what i read offsets are only high when channel is active . and not just one channel . 400mv offset .
                                      i haven't studied whether it cuts the speaker off or mutes the input when not selected .
                                      Last edited by petehall347; 08-07-2020, 08:22 AM.

                                      Comment


                                        #20
                                        Re: Yamahaha RX-V679 DC PRT High

                                        SR: 0.353
                                        SL: 0.302
                                        C: 0.300
                                        FR: 0.358
                                        FL: 0.305
                                        SBR: -0.009
                                        SBL: 0.814

                                        Those measurements are with all channels selected.

                                        waiting on it to kick off so I can measure the jumper now.
                                        Attached Files

                                        Comment

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