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Yamaha A-520 HiFi amplifier

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    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

    #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


      #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


        #4
        Re: Yamaha A-520 HiFi amplifier

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

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          #5
          Re: Yamaha A-520 HiFi amplifier

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

          Comment


            #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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