Hitachi 3d7 mk2 boombox hum/noise

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  • IVH
    New Member
    • Sep 2016
    • 3
    • Attention seeker
    #1

    Hitachi 3d7 mk2 boombox hum/noise

    Hi guys,
    I'm currently restaurating a hitachi 3d7 MKII boombox, it is going well, except for one thing: there is a hum hearable while listening at any volume (it gets louder when turning up the volume).
    In order to troubleshoot the bad cap(s) I was thinking of temporarily mounting (I mean holding against) a good cap in parallel with another to check if the hum decreases (or changes).
    Is this possible without damaging the boombox ? and can this be effective ?
    I'm not quite confortable with replacing every cap even though only 1 has probably failed. (I don't have enough in stock and this project is getting quite expensive now).
    Thank you in advance !
    Idris
    Last edited by IVH; 09-18-2016, 01:38 AM.
    Tags: None
    • stj
      Great Sage 齊天大聖
      • Dec 2009
      • 31015
      • Albion
      #2
      Re: Hitachi 3d7 mk2 boombox hum/noise

      does it do the same on batteries?

        Comment

        • IVH
          New Member
          • Sep 2016
          • 3
          • Attention seeker
          #3
          Re: Hitachi 3d7 mk2 boombox hum/noise

          Originally posted by stj
          does it do the same on batteries?
          Thank you for the reply !
          Sorry, I forgot to mention this:
          -it happens on the left and right channel + with headphones
          -noticeable when on batteries
          -the noise gets louder when turning the volume up
          -it can be filtered out using the equalisers
          -it is even noticable when nothing is connected (tape deck disconnected from main board, no line-in connected)
          -clearly hearable when playing music through the cassette deck or line in.
          -the resistance between the ground of the power supply is 0 Ohm to all 'grounds' I measured on the board

          The problem might lay in the pre amp, but I don't know where it's located as I don't have a service manual.
          That's why I wanted to check it the way I described it in the first post.

            Comment

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