2275 preamp noise

Discussion in 'Marantz Audio' started by Mico, Jun 14, 2018.

  1. Mico

    Mico Active Member

    Messages:
    345
    Location:
    Montreal
    Got 2275 with strong humming noise, so strong I was sure that big filter caps were done.
    Upon replacing them noise was a bit lower but still there. Than tested pre and power amp sections, first connecting preamp output to 2238B - and it blew 2A fuse on 2238B`s PS board instantly! 2238B lights went off but rest was working and buzzing was there. In reversed scenario, 2238B preamp into 2275`s Main in, everything worked fine. Noise is there as soon as relay clicks and volume control does not change it until around 10`clock when it gets really nasty. Did not look into preamp board for obvious issues yet, what would be a good point to start the investigation?
     
    Last edited: Jun 14, 2018

     

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  2. FinalVinyl

    FinalVinyl Active Member

    Messages:
    115
    replace all the capacitors. if that doesn't work replace the transistors
     
  3. spark1

    spark1 Super Member

    Messages:
    1,213
    Location:
    The Great Midwest
    My truck has a rattle. Should I replace the motor, transmission, exhaust system, tires and suspension?
     
    Last edited: Jun 17, 2018
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  4. Aaron99

    Aaron99 AK Subscriber Subscriber

    Messages:
    296
    Location:
    Vancouver WA.
    Nah, just replace the wipper blades and you'll be golden....

    If that doesn't work. Replace all the solder.... ;)
     
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  5. spark1

    spark1 Super Member

    Messages:
    1,213
    Location:
    The Great Midwest
    Is the humming noise through the speakers or coming from the unit itself? Does it make this noise even with no input devices connected to it (turntables, CD players, etc)?
     
  6. Mico

    Mico Active Member

    Messages:
    345
    Location:
    Montreal
    Noise is constant and only in speakers/ headphones , regardless of input existence or volume level. Frying fuse on another amp through pre-out to main-is a bit worrying.
     

     

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  7. Osibisa

    Osibisa AK Subscriber Subscriber

    Messages:
    296
    Location:
    New Jersey
    Going out on a limb, but soon after servicing my 2275 a loud hum developed in the right channel as soon as the relay closed. Turned out to be a loose connection to the power amp module, deoxit applied to pins and connector hum disappeared.
    You might want to try disconnecting the amp modules to see if you still get hum through headphones if you haven't tried that yet. I'm going to assume that the bottom cover is attached right?
     
  8. Steven Tate

    Steven Tate AK Subscriber Subscriber

    Messages:
    2,808
    Location:
    N. Richland Hills, TX
    Very good point. Also, the big connector to the Pre amp board is notorious for all kinds of noises that Deoxit can tame.
     
  9. Mico

    Mico Active Member

    Messages:
    345
    Location:
    Montreal
    At the end it was a bad cap (or caps) on the power supply board. I noticed PS was looking pretty bad but was not expecting it could affect only preamp section.
    Problem solved, lesson learned...
     

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  10. Osibisa

    Osibisa AK Subscriber Subscriber

    Messages:
    296
    Location:
    New Jersey
    If you haven't already done so, I would strongly suggest you recap the entire PS board and move the ceramic resistor away from the cap shown in your picture.
    Good job nonetheless for finding the culprit.
     
  11. Mico

    Mico Active Member

    Messages:
    345
    Location:
    Montreal
    That`s how it looks now :) Big caps are upgraded from 13.000uF/55V to 15.000uF/63V
     

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    Last edited: Jul 10, 2018

     

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