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CR-2020 Intermittent Hum

Discussion in 'Yamaha' started by aeyb701, Mar 19, 2017.

  1. aeyb701

    aeyb701 Member

    Messages:
    91
    Location:
    Peterborough, Ontario, Canada
    I have a Yamaha CR-2020 I found at a waste station last year, and since then I've performed the service bulletin(s) and between me and a technician whom I trust hav replaced many capacitors in the power supply, hoping to sort a 120Hz (I think, maybe it's 60) hum. The hum is not there until, on another part of the room circuit, I turn on one of those electric liquid-filled heaters, the ones that look like upright wall radiators.
    It also comes when I have BOTH leads of a 300-ohm FM antenna hooked up, but not if it's just one lead.
    It is there regardless of input, and even with no inputs connected.
    It is in both channels.
    It increases with the volume control, and is not there when set at zero.
    Oddly it also increases when the low-filter is flicked up to the 70Hz position.
    With the case off and using the end of a fine paint brush to press around the hum may vary with the position of groups of wires ( I do not know which as they're so many running in bunches).
    Everything else is perfect.
    Even replaced the filter caps with new Nichicons since the power supply board was lifted for other cap replacement and it's a bear to disassemble.
    Given the above behaviour, especially with the way an antenna is connected, I'm starting to think it's a ground issues more than any cap.
    Anyone have any ideas?
    Thanks,
    Jon Archibald
    Indian River, Ontario, Canada
     
  2. avionic

    avionic " Black Knights" Subscriber

    Messages:
    33,734
    Location:
    Fort Dodge, Iowa cornfield
    Is this a 220v unit ?
    Nevermind 120v standard.
     
  3. avionic

    avionic " Black Knights" Subscriber

    Messages:
    33,734
    Location:
    Fort Dodge, Iowa cornfield
    Did you try reversing the AC mains plug 180° ?
     
  4. aeyb701

    aeyb701 Member

    Messages:
    91
    Location:
    Peterborough, Ontario, Canada
    Thanks-you for chiming in Avionic.
    Yes. Same thing with AC plug reversed, but the fm antenna fully connected didn't induce the hum this time.
    Oddly someone had marked the polarity of the plug for some reason, perhaps ground loops encountered with other components.
    Maybe a cold solder joint. Pulling all the Pcb's would be a job, but I could try grounding the grounds of each board via alligator wire to the chassis.
    I've no experience with an oscilloscope but do have LCR and digital multi meters.
     

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