Fender PD-250 Passport has low audio output Right Side

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  • tfs2015
    Senior Member
    • Feb 2015
    • 135
    • USA

    #21
    Re: Fender PD-250 Passport has low audio output Right Side

    What does the BIAS and OFFSET adjustments control? The reason I am asking is it looks like they could have been moved from their original factory set positions.
    Computer and Small electronics troubleshooting and repair

    Comment

    • budm
      Badcaps Legend
      • Feb 2010
      • 40746
      • USA

      #22
      Re: Fender PD-250 Passport has low audio output Right Side

      The BIAS pot is for setting the current flowing through the output transistor (with out input signal) in idling condition, the set point is set for Class A/B mode for this amplifier.
      The OFFSET adjustment pot is for setting the DCV at the out put to be at 0V so at no signal the speaker will be seeing 0VDC on the speaker coil.
      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

      • tfs2015
        Senior Member
        • Feb 2015
        • 135
        • USA

        #23
        Re: Fender PD-250 Passport has low audio output Right Side

        So assuming these are set right should I suspect a bad transistor or capictor. Need to test transistors without voltage applied?
        Computer and Small electronics troubleshooting and repair

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #24
          Re: Fender PD-250 Passport has low audio output Right Side

          You do need to test the transistors and diodes (do the search on how to test transistors and Diodes), resistors (check the values and its condition) without power applied to the unit. Any suspect parts that tested bad should then be removed off the board and test again.
          This is not really for beginner that do not have enough knowledge yet on how the devices function. Do you know how to read the schematic and have proper tools?
          Last edited by budm; 05-15-2015, 11:07 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

          • tfs2015
            Senior Member
            • Feb 2015
            • 135
            • USA

            #25
            Re: Fender PD-250 Passport has low audio output Right Side

            yes I can read the schematic and I have a solder iron and DMM. I will report back later on what I find. Thank you for the help if you can think of anything else please let me know.

            Thanks
            Tom S.
            Computer and Small electronics troubleshooting and repair

            Comment

            • tfs2015
              Senior Member
              • Feb 2015
              • 135
              • USA

              #26
              Re: Fender PD-250 Passport has low audio output Right Side

              As i increased the volume on the right right side output channel, I noticed that the sound became distorted and not clear. It sounded more like "thud" sounds then it did music. Which leads me to believe that when Q217 was replaced that the electrical characteristics of that one and original are not the same and therefore either the offset/bias or both needs to reset for this unit to function properly. Is that a good conclusion or is there more that I should be looking at.
              Computer and Small electronics troubleshooting and repair

              Comment

              • tfs2015
                Senior Member
                • Feb 2015
                • 135
                • USA

                #27
                Re: Fender PD-250 Passport has low audio output Right Side

                Looks like my problems went from bad to worse well checking things out today on the amp board. Looks like if the power amp to power supply is connected the protect light comes on. Otherwise if it is not plug in the unit is fine. Please help!!!!! Thank you

                Tom S.
                Computer and Small electronics troubleshooting and repair

                Comment

                • tfs2015
                  Senior Member
                  • Feb 2015
                  • 135
                  • USA

                  #28
                  Re: Fender PD-250 Passport has low audio output Right Side

                  After doing more component testing and checking, there seems to be extra components added to the board and some of the diodes are missing. I am playing with the idea of replacing the whole board or just all of the components which ever is cheaper. Once I get that done I am going to need help to set the OFFSET for the amp's left and right sides and also the BIAS adjustments without the help of an O'scope. Any help would be appreciated.

                  Thanks
                  Tom S.

                  p.s. I want to use this in parades this summer hooked up to my truck to play music and make announcements.
                  Computer and Small electronics troubleshooting and repair

                  Comment

                  • tfs2015
                    Senior Member
                    • Feb 2015
                    • 135
                    • USA

                    #29
                    Re: Fender PD-250 Passport has low audio output Right Side

                    I have two blown output transistors. One one the left channel and one on the right channel also had some thermal damage to the emitter resisters on both channels. I have also found that the caps c212 and 213 that were supposed to be 10uF 63v had been replaced with 4 1200uF 63v caps. So I was wondering should I keep pulling the transistors and caps off of the board to check or just order the new output transistors?

                    Thanks
                    Tom S.
                    Computer and Small electronics troubleshooting and repair

                    Comment

                    • tfs2015
                      Senior Member
                      • Feb 2015
                      • 135
                      • USA

                      #30
                      Re: Fender PD-250 Passport has low audio output Right Side

                      Need help to adjust BIAS and OFFSET on this amp now that I got it working.

                      Thanks
                      Tom S.
                      Computer and Small electronics troubleshooting and repair

                      Comment

                      • tfs2015
                        Senior Member
                        • Feb 2015
                        • 135
                        • USA

                        #31
                        Re: Fender PD-250 Passport has low audio output Right Side

                        Everything is working good now, except a pop sound is heard when unit is shut off with speakers plugged in. Thanks everyone for the help.
                        Computer and Small electronics troubleshooting and repair

                        Comment

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