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NAD 4020A FM tuning

Discussion in 'Tuners' started by breakfastipa, Aug 9, 2017.

  1. breakfastipa

    breakfastipa Member

    Messages:
    54
    Hi, I'm trying to adjust the FM tuning on my 4020A and it appears to be off by ~1-2Mhz. I don't have an oscilliscope or anything to verify the tuning. It's a bit difficult to tell by the service manual which adjustment I need to make (I was going to use by trial and error, using a good station signal) to try to correct this. According to the SN#, I have the new version. Thanks for your help

    Link to service manual: http://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Nad-4020-A-Service-Manual.pdf
     

     

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  2. chazix

    chazix AK Subscriber Subscriber

    Messages:
    1,147
    Location:
    Groton MA
    That is much more than would be expected from electronic mis-adjustment. If you tune from stop to stop, does the pointer come close to the outermost tics on the tuning scale? If not, then I think there is a mechanical misalignment.

    Another sign of a mechanical misalignment if if the tuning pointer is "off" by about the same linear distance for either AM or FM.

    I can't say I recommend it, but if you decide to plunge ahead with electronic adjustments, the one marked TC3 (on the "old" layout, but the "new" layout certainly seems to have the same adjustment point, though it's either unmarked or obscured) is your best bet.

    (I urge you not to try making any of the "L(something)" adjustments, nor the "IFT1". These are inductive (coil-constructed) parts. Generally speaking, adjusting coils without a tool specifically designed for that purpose will result in frustration at best and is very, very likely to ruin the coils.)

    Cheers,

    chazix
     
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  3. breakfastipa

    breakfastipa Member

    Messages:
    54
    This advice worked perfectly, I was able to adjust it to the signal using the TC3 point. Thank you!
     
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  4. chazix

    chazix AK Subscriber Subscriber

    Messages:
    1,147
    Location:
    Groton MA
    Great - congrats!
     
  5. Boyter

    Boyter New Member

    Messages:
    3
    Hi Chazix,
    I signed up to AK to thank you for your tip. My 4020A was off so I used your advice to adjust the TC3, plus adjusting the pulley to get it pretty close.

    What does TC3 do? It seemed like it was changing the spread of the frequencies. I mechanically adjusted so the lowest station was correct and moved to the highest station and adjusted TC3 until it lined up.
     
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  6. chazix

    chazix AK Subscriber Subscriber

    Messages:
    1,147
    Location:
    Groton MA
    This might be too short an answer to be terribly meaningful, but TC3 is a "trimmer" capacitor that fine-tunes one section of the big air-vane main tuning capacitor. TC3 will have most effect on higher frequencies, so your procedure of lining up mechanically at low frequencies and then tweaking TC3 is about as good a procedure as would be feasible most DIYers.

    Glad it helped, and welcome to AK!

    chazix
     
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  7. Boyter

    Boyter New Member

    Messages:
    3
    I'm shocked, I did something right! :)
     

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