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Issue setting dc offset on Marantz 4240 quad receiver.

Discussion in 'Marantz Audio' started by saabracer23, Nov 8, 2018.

  1. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
    1,001
    Location:
    Salem, Oregon
    I’ve just rebuilt a Marantz 4240, so far I’ve set bias. That was pretty straight forward and easy. Now onto setting dc offset. The manual says to put the neg lead to pin 706 and pos to 715/716. Only my boards don’t have a 715 or 716. There is a place for them but nothing there. There are fuses in that area that aren’t shown in the manual. So I put my leads at the speaker outputs. The front channels were set no problem.

    The issue is with the rear channels. Does the amp mode need to be in a specific spot? I just get very low readings around 2 mV in each channel, but the variable resistor does absolutely nothing. When I grab the lead cables while it’s in the rear outputs it’ll shoot up to like 300 mV. What am I doing wrong?

    Dan
     

     

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  2. wurlyman

    wurlyman Active Member

    Messages:
    269
    Location:
    Sacramento, CA
    It looks like it could be J727 and J728, the outside edges of the fuses.
     
  3. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
    1,001
    Location:
    Salem, Oregon
    Should I remove the fuses? I tried that and I get 28v and again the trimmers do nothing. So I checked the fronts that way and they too were measuring 28v dc at the outside of the fuse yet around 1 mV at the speaker output.

    Dan
     
  4. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
    1,001
    Location:
    Salem, Oregon
    Resolved, took a board out to get a better look at the pin numbers.

    Dan
     
    wurlyman likes this.
  5. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
    1,001
    Location:
    Salem, Oregon
    Nm
    Dan
     
    Last edited: Nov 9, 2018

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