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Another C-70 channel dropout issue

Discussion in 'Yamaha' started by sjsingle1, Sep 23, 2018.

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  1. sjsingle1

    sjsingle1 New Member

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    Newbie here, but long time audio enthusiast. I have a C-70 I bought when stationed in europe in the 80s ( I loaded up on lots of low priced high fi !! ) and its one of my favs. In the 90s it developed a channel issue that a local worthless repair shop fixed with a install of a new balance pot ( knob ? ) it did not fix the problem so into non use it went for all these yrs. Now I would like to fix it up to pass on to my son so off to the best local repair shop I can find. First shop was no better than the one I used in the 90s, so back to searching, so find success in my search for a shop and drop it off for a overhaul ( recap and so forth ) I quickly find the relays...HB2E-DC24V ..are hard to find but managed to get my hands on some. So everything under the hood is spanking new and I pick it up only to later find I STILL have my drop out issue, to be honest I just casually mention this issue and hope the overhaul does the trick.

    My repair guy is the best local to me ( he is great with tube macintosh's FWIW ) but he is having a hard time fixing this problem, anything I can tell him to point him in the right direction or should I just send it to someone anybody can recommend who has experience in these pre amps ?
     

     

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  2. sjsingle1

    sjsingle1 New Member

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    Oh...I only get the dropout with the tone control engaged
     
  3. mbz

    mbz Super Member

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    Certainly, intermittent problems are hard to track down. The relays do have a history of going internittent. Mine are
    due to arrive in the next few days, sourced off ebay from china, not much hope. However of greater concern are all the dry solder
    joints in the C-70 (well, mine at least), about 50% of the joints looked suspect, worst case I've seen. Google dry solder joints
    for pix however your tech will know this.
     
    Oldsansui441 likes this.
  4. avionic

    avionic " Black Knights " Subscriber

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    Welcome to AK.. Have your tech look at SW503. It will need to be disassembled and cleaned.
    It's a solenoid operated switch. Located under the (Tone Control Circuit board 2) on the left side main board.
     
    Last edited: Sep 23, 2018
  5. sjsingle1

    sjsingle1 New Member

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    SW503 ? a member here ?
     
  6. avionic

    avionic " Black Knights " Subscriber

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    Red X marks the switch DSC04228.JPG
     

     

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  7. avionic

    avionic " Black Knights " Subscriber

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    No .. SW503 is switch 503
     
  8. sjsingle1

    sjsingle1 New Member

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    Oh ...OK....lol.....I went to electronics school at Keesler AFB but damm if I can remember anything I learned there

    my tech did mention he had to pull up the tone control board from under the main board and what a PITA is was
     
  9. avionic

    avionic " Black Knights " Subscriber

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    I'm going to tell you flat out. Just trying to spray cleaner inside that switch will not get it clean. It needs to be disassembled.
     
  10. avionic

    avionic " Black Knights " Subscriber

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    I went to Lowry AFB --- F/FB-111 and F-15 electronic warfare component specialist.
     
  11. sjsingle1

    sjsingle1 New Member

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    is it a switch ? relay? or ?

    did you have this problem on your C70 ?

    I went to Lowery AFB too.....for Disaster Preparedness school
     

     

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  12. avionic

    avionic " Black Knights " Subscriber

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    Solenoid operated switch. I repair and refurb C-70's among other Yamaha separates quite frequently.
    Highly recommend replacing all 8 of those HB2 relays.;)
     
  13. sjsingle1

    sjsingle1 New Member

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    I had all those HB2s replaced !!
     
    Last edited: Sep 23, 2018
  14. avionic

    avionic " Black Knights " Subscriber

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    OK.. Wasn't sure if you replaced a couple or all of them.
     
  15. avionic

    avionic " Black Knights " Subscriber

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    What's your geographic location?
     
  16. sjsingle1

    sjsingle1 New Member

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    texas, fort worth

    happened to have those HB2 right in front of me at the computer
     

     

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  17. sjsingle1

    sjsingle1 New Member

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  18. avionic

    avionic " Black Knights " Subscriber

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    Them be the ones.
     
  19. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    +1 on this, these Yamaha's are notorious for poor joints. Currently working on a C-85 which has already taken many hours of reflowing also. Certainly not saying it couldn't be the switch that avionic suggested though.

    Does your channel drop out occur on any input or only one?
     
    mbz likes this.
  20. mbz

    mbz Super Member

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    Good question.
     

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