1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

Fisher 400 no FM mono

Discussion in 'Fisher' started by curtsad17, Aug 11, 2018.

  1. curtsad17

    curtsad17 Member

    Messages:
    73
    Location:
    Media, PA
    My 400 is sounding wonderful but I have no FM mono output. I replaced the suspect 1 uf in the MPX and corrected the eye dance. In mono the eye retracts and does react to tuning but modulates a little. If I had to guess ( remember I am a novice) I would think the issue is after or R28 which does not leave much including the selector switch.
     

     

    Please register to disable this ad.

  2. Dave451

    Dave451 AK Subscriber Subscriber

    Messages:
    1,179
    Location:
    Philly area
    Have you replaced C41, 8uF cap in ratio detector circuit? That one should be done as well.
     
  3. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,773
    Location:
    Ball Ground, GA
    If you've got a good FM Stereo signal in both channels, but no mono signal in either channel, then it's doubtful that the problem is the selector switch. More likely, at some point in the path of R28, the signal is either broken, or shorted to ground after R28 (on the selector switch side). I'd wiggle and poke about that signal path -- as you say, not much otherwise that can cause this.

    Dave
     
  4. curtsad17

    curtsad17 Member

    Messages:
    73
    Location:
    Media, PA
    It was a bad solder joint R28..
     
  5. Dave451

    Dave451 AK Subscriber Subscriber

    Messages:
    1,179
    Location:
    Philly area
    Well spotted!
     
  6. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,773
    Location:
    Ball Ground, GA
    Glad you found it!

    Dave
     

     

    Please register to disable this ad.

  7. Tim D

    Tim D AK Subscriber Subscriber

    Messages:
    1,412
    Location:
    Melbourne, FL

Share This Page