Panasonic radio plays only one side

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  • Behemot
    Badcaps Legend
    • Dec 2009
    • 4845
    • CZ

    #1

    Panasonic radio plays only one side

    Got this radio where only one side plays. The amplifier section seems pretty simple, there is basically LA4705N responsible for everything. Anybody has some experience with that? Is it the main suspect?
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  • stj
    Great Sage 齊天大聖
    • Dec 2009
    • 31002
    • Albion

    #2
    Re: Panasonic radio plays only one side

    link the left & right input pins to get your answer.

    Comment

    • Behemot
      Badcaps Legend
      • Dec 2009
      • 4845
      • CZ

      #3
      Re: Panasonic radio plays only one side

      Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

      Exclusive caps, meters and more!
      Hardware Insights - power supply reviews and more!

      Comment

      • stj
        Great Sage 齊天大聖
        • Dec 2009
        • 31002
        • Albion

        #4
        Re: Panasonic radio plays only one side

        if it's a stereo chip and you link the left & right input pins, you can see if you get sound from both speakers.

        otherwise, feed some sound through it and scope the inputs to the amp section.

        Comment

        • stj
          Great Sage 齊天大聖
          • Dec 2009
          • 31002
          • Albion

          #5
          Re: Panasonic radio plays only one side

          link pins 2 & 7
          Attached Files

          Comment

          • budm
            Badcaps Legend
            • Feb 2010
            • 40746
            • USA

            #6
            Re: Panasonic radio plays only one side

            Using capacitor so you will not cause Voltage offset.
            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

            • Behemot
              Badcaps Legend
              • Dec 2009
              • 4845
              • CZ

              #7
              Re: Panasonic radio plays only one side

              Originally posted by budm
              Using capacitor so you will not cause Voltage offset.
              Some ceramic?
              Originally posted by stj
              link pins 2 & 7
              But why inputs? Why not outputs?
              Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

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              • stj
                Great Sage 齊天大聖
                • Dec 2009
                • 31002
                • Albion

                #8
                Re: Panasonic radio plays only one side

                it's a btl amp, designed for bridging - if you link the outputs you blow the chip because they are out of phase.

                it wouldnt prove anything anyway.
                by shorting the inputs to the amp, you are finding if the channel is missing before, or inside/after the amp chip.

                Comment

                • momaka
                  master hoarder
                  • May 2008
                  • 12170
                  • Bulgaria

                  #9
                  Re: Panasonic radio plays only one side

                  Originally posted by budm
                  Using capacitor so you will not cause Voltage offset.
                  Or you can link the pins on the input coupling capacitors, not on the side that goes to the chip (i.e. pins 2 and 7) but their other side. That way you won't need to any caps to test the circuit and it works just the same .

                  Comment

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: Panasonic radio plays only one side

                    If the input side of the caps are connected to the pots then it will be fine but if they are connected to the active devices such as the Collector of the Transistors (or the Emitter as in Emitter follower, or output of the OP-AMPs) then that can be the problem since you will tie the Collector of the Left and right Transistors together. Better find out how they are being used first before doing any direct connection.
                    Last edited by budm; 06-08-2015, 10:56 PM.
                    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

                    • popeye
                      Senior Member
                      • May 2011
                      • 155

                      #11
                      Re: Panasonic radio plays only one side

                      Originally posted by Behemot
                      Got this radio where only one side plays. The amplifier section seems pretty simple, there is basically LA4705N responsible for everything. Anybody has some experience with that? Is it the main suspect?
                      Hi I take it this is a stereo amp then you dont even need a schematic because all you need is in front of you check between the componant measurements
                      from one side of the out put to the other working one if your fault is not there check you are getting the correct inputs if in puts are ok then problem is with the ic if not you know what you should be getting from the working side so compare.

                      Comment

                      • Behemot
                        Badcaps Legend
                        • Dec 2009
                        • 4845
                        • CZ

                        #12
                        Re: Panasonic radio plays only one side

                        It does the same for all settings (radio, CD player) that's why I think input is OK as it goes from different sources with same result.

                        The headphone output usually goes through amplifier or not? If not I can try some and in such case I guess I can call input OK too?
                        Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

                        Exclusive caps, meters and more!
                        Hardware Insights - power supply reviews and more!

                        Comment

                        • momaka
                          master hoarder
                          • May 2008
                          • 12170
                          • Bulgaria

                          #13
                          Re: Panasonic radio plays only one side

                          Originally posted by budm
                          If the input side of the caps are connected to the pots then it will be fine but if they are connected to the active devices such as the Collector of the Transistors (or the Emitter as in Emitter follower, or output of the OP-AMPs) then that can be the problem since you will tie the Collector of the Left and right Transistors together.
                          Most of the time, they are connected to an electronic switch that toggles which source (i.e. radio, tape, or CD) go to the amp. After that, there is usually a resistor, the amp input coupling caps, and the amp itself. At least that's what I have seen in most "modern" (90s +) units.

                          But I agree. It is better to check what is connected to what before blindly jumpering stuff.

                          Originally posted by Behemot
                          The headphone output usually goes through amplifier or not? If not I can try some and in such case I guess I can call input OK too?
                          In many cases it does.

                          So yes, check with headphones. If you do get sound from both channels with headphones, it could be the headphone jack switching contacts are messed up or just dirty.

                          The way the output on most boomboxes and "mini" stereo systems is done is you have the outputs from the power amp going to the headphone jack. The headphone jack has switching contacts. If you plug in headphones, the output goes to the headphones and mutes the speakers. If you unplug the headphones, the contacts in the headphone jack switch to route the output to the speakers. Inexpensive stereo PC speakers also do it this way.
                          Last edited by momaka; 06-09-2015, 07:18 AM.

                          Comment

                          • stj
                            Great Sage 齊天大聖
                            • Dec 2009
                            • 31002
                            • Albion

                            #14
                            Re: Panasonic radio plays only one side

                            look at the schematic in the datasheet.

                            Comment

                            • budm
                              Badcaps Legend
                              • Feb 2010
                              • 40746
                              • USA

                              #15
                              Re: Panasonic radio plays only one side

                              You have the scope so that will be so simple to trace where the signal gets lost at, GOOD AC Volt meter will do as well.
                              Last edited by budm; 06-09-2015, 09:04 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

                              • stj
                                Great Sage 齊天大聖
                                • Dec 2009
                                • 31002
                                • Albion

                                #16
                                Re: Panasonic radio plays only one side

                                is it fixed yet?

                                i could fix this while waiting for the kettle to boil.

                                Comment

                                • Behemot
                                  Badcaps Legend
                                  • Dec 2009
                                  • 4845
                                  • CZ

                                  #17
                                  Re: Panasonic radio plays only one side

                                  You got teleport device?
                                  Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

                                  Exclusive caps, meters and more!
                                  Hardware Insights - power supply reviews and more!

                                  Comment

                                  • momaka
                                    master hoarder
                                    • May 2008
                                    • 12170
                                    • Bulgaria

                                    #18
                                    Re: Panasonic radio plays only one side

                                    Originally posted by stj
                                    is it fixed yet?

                                    i could fix this while waiting for the kettle to boil.
                                    Not unless it is a "modified" kettle by PhotonicInduction

                                    https://www.youtube.com/watch?v=dDLw1Rx_cAI

                                    Comment

                                    • stj
                                      Great Sage 齊天大聖
                                      • Dec 2009
                                      • 31002
                                      • Albion

                                      #19
                                      Re: Panasonic radio plays only one side

                                      seriously, probe pins 2 & 7 for audio.
                                      if it's on both, check between the ic and speakers - and check speaker coils.
                                      no issues? then the chip is bad.

                                      missing audio on one of the pins first checked? then trace it back.

                                      Comment

                                      • Behemot
                                        Badcaps Legend
                                        • Dec 2009
                                        • 4845
                                        • CZ

                                        #20
                                        Re: Panasonic radio plays only one side

                                        I am just moving from shared shop to my own room so I already have 2/3 of my stuff moved and 1/3 is messed everywhere around. Don't even have room for the radio on my table, it is quite huge and I don't want to mess with my O-scope ATM. Thanks for the input so far, I'll try when I am moved completelly. I am exhausted every day last week…
                                        Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

                                        Exclusive caps, meters and more!
                                        Hardware Insights - power supply reviews and more!

                                        Comment

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