Yamaha A-520 HiFi amplifier

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  • Nevillet
    Badcaps Veteran
    • Sep 2019
    • 272
    • United Kingdom
    #1

    Yamaha A-520 HiFi amplifier

    Hi All,

    I have a Yamaha A-520 that has no sound output.

    I notice after power up the protection protection relay does not click in.

    I'd appreciate any pointers on where to start.

    Many thanks.

    Service Manual below:
    https://www.badcaps.net/forum/attach...1&d=1641841819
    Attached Files
    Tags: None
    • stj
      Great Sage 齊天大聖
      • Dec 2009
      • 30997
      • Albion
      #2
      Re: Yamaha A-520 HiFi amplifier

      first put a resistor and led across the relay coil to see if it's being powered but bad.

        Comment

        • R_J
          Badcaps Legend
          • Jun 2012
          • 9535
          • Canada
          #3
          Re: Yamaha A-520 HiFi amplifier

          Check the DC voltage on TPR0 or on the output coil L105 and L106. You likely have a bad output causing the protection circuit to activate to protect the speakers

            Comment

            • CapLeaker
              Leaking Member
              • Dec 2014
              • 8133
              • Canada
              #4
              Re: Yamaha A-520 HiFi amplifier

              Probably dc on the output = blown transistor(s).

                Comment

                • R_J
                  Badcaps Legend
                  • Jun 2012
                  • 9535
                  • Canada
                  #5
                  Re: Yamaha A-520 HiFi amplifier

                  .
                  Last edited by R_J; 01-10-2022, 04:32 PM.

                    Comment

                    • Nevillet
                      Badcaps Veteran
                      • Sep 2019
                      • 272
                      • United Kingdom
                      #6
                      Re: Yamaha A-520 HiFi amplifier

                      Hi,

                      I got back to the amp this morning and have a few developments to report:

                      I have a series 120W tungstan lamp in series with the mains (240V) supply.

                      On power up the amp draws lots of current to the point that R207 smokes (180Ω 1/4W)

                      After a rapid disconection I desoldered the 4 main output transistors to test them (TR121,122,123,124) and all tested OK. (C3182x2 & A1265 x2)

                      I also tested the two smaller transistors mounted between these pairs on the heatsink. (TR115/116 ) Unfortunatly I managed to break a leg off of one of these and now need to source a replacement 2SC2240. I'd appreciate suggestions for a substitute..

                        Comment

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