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.
  • stj
    Great Sage 齊天大聖
    • Dec 2009
    • 30985
    • 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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