Fisher 400 Rebuild Project

Discussion in 'Fisher' started by tekuhn, Apr 10, 2018.

  1. tekuhn

    tekuhn Active Member

    Messages:
    103
    Location:
    East Texas
    I have not checked any voltages yet. I wanted to have at least one replacement for each tube type used in the tuner which I will in a couple days. You might very well be onto something there. I noticed that when I flex the chassis slightly while listening to the static, I can create some pops and changes in the volume of the static. If I select an audio source like AUX or Tape Mon, I do not get any noises doing the same. I was picking up the unit to put it on it's side which is how I flexed it and noticed that issue. That's the first thing I'll look at are heaters and socket voltages. Thanks for your suggestions and insight!
     

     

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  2. tekuhn

    tekuhn Active Member

    Messages:
    103
    Location:
    East Texas
    Tubes arrived today, and turns out V2 (6AB4) was bad. I now have a strong clear signal, although my station choices are very limited where I live. When I switch from mono to stereo, the beam indicator narrows as expected, although I don't really hear much difference in the audio. If there is any separation happening, it's very subtle. I will still go through the basic non-instrument FM alignment process, but I suspect that the multiplex module needs calibration. The separation pot is fully rotated clockwise against the stop which I doubt is the factory setting. I rarely will use the tuner, but did want it to work which it now does!

    Mono
    IMG_3871.JPG

    Stereo
    IMG_3873.JPG

    Separation Pot.......
    IMG_3872.JPG
     
  3. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,416
    Location:
    Ball Ground, GA
    No way that is a correct setting. Try setting it at about the 6:00 position and see if you can't hear some separation then.

    Congrats on getting the tuner going!

    Dave
     
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  4. tekuhn

    tekuhn Active Member

    Messages:
    103
    Location:
    East Texas
    I had already tried slowly rotating it through the full range of travel and didn't hear it change. I'll put a meter on it and make sure it's working - might need cleaning. I need some Beatles or other group that was recorded with hard-panned instruments to help me out! :)
     
  5. thornev

    thornev Active Member

    Messages:
    373
    Location:
    Mid Hudson Valley, NY
    Did you do the listening with headphones? You're guaranteed to hear signal separation with headphones assuming that the pot works correctly. Thorne
     
  6. fred soop

    fred soop Super Member

    Messages:
    1,915
    Scanning across the band with the scope in X-Y mode, very little of the crap that passes for alleged music has much separation, so the problem may not be totally your receiver.
     
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  7. tekuhn

    tekuhn Active Member

    Messages:
    103
    Location:
    East Texas
    Thanks, Thorne. I remember you saying you did yours that way. I cleaned the pot and used headphones. I do have mild separation, but I’m not convinced it’s as much as expected. I’m going to try a few more things.
     
  8. tekuhn

    tekuhn Active Member

    Messages:
    103
    Location:
    East Texas
    Oh yeah, one more surprise. The headphone jack has the left and right channels reversed. Maybe the wiring for 1/4” TRS wasn’t standardized yet in ‘65?
     
  9. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,416
    Location:
    Ball Ground, GA
    This is one case where the old addage is actually correct: "They're all like that!" And they are. You need to swap the resistors at the headphone jack to correct the problem.

    Dave
     
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  10. tekuhn

    tekuhn Active Member

    Messages:
    103
    Location:
    East Texas
    I'm a little confused about the "non-instrument" KM-60 alignment instructions and where the error is. Here is a summary of the instructions if someone wouldn't mind commenting on what needs to be changed.

    1 - Selector on FM Mono - all adjustments are for maximum meter reading
    2 - Tune to weak station reading between 1 and 2 (will guess using tuning beam)
    3 - Adjust limiter coil (Z4) from top
    4 - Adjust 3rd IF transformer (Z3) from bottom and then top
    5 - Adjust 2nd IF transformer (Z2) from bottom and then top (may not see increase in meter if 3rd and 4th stages already limiting)
    6 - Adjust tuning knob to ensure still on maximum signal strength
    7 - Repeat steps 3 thru 5 in same order
    8 - Tune between stations for hiss
    9 - Repeat steps 3 thru 5 in same order
    10 - Adjust 1st IF transformer (Z1) from bottom and then top
    11 - Adjust Ratio Detector (Z5) from bottom and then top

    Do I need to reverse the order on the last step for Z5 - top and then bottom?

    Thanks!

    Tom
     
  11. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,607
    Location:
    Glen Burnie Md.
    No. The swap is taken into account in #3.
    Then add 3a. Adjust z4 bottom for maximum closure on V7 (em-84a tube).
    Then follow the rest of the directions. Thats how I do mine and get good results.
     

     

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  12. tekuhn

    tekuhn Active Member

    Messages:
    103
    Location:
    East Texas
    Cool. I was under the impression that one of the steps had top and bottom reversed. Thanks for the clarification. I had to dig around for my nylon hex tools and the size I need is missing, of course. Amazon will be delivering Monday.
     
  13. thornev

    thornev Active Member

    Messages:
    373
    Location:
    Mid Hudson Valley, NY
    This is interesting. Dave told me to adjust starting at Z1 and going forward. Larry is saying to adjust starting with Z4 and going backwards (except for Z5). I'm curious about the differences in results going backward versus forward.
     
  14. tekuhn

    tekuhn Active Member

    Messages:
    103
    Location:
    East Texas
    The steps I posted came right out of the KM-60 service manual only I added the names of the coils. The manual just refers to them as limiter coil, 1st, 2nd, and 3rd IF coil, and ratio detector coil. I substituted what I believe to be the correct component number using the schematic. The KM-60 uses different numbers. I made the assumption that the 1st IF coil is the one closest to the front-end (Z1). Since it doesn't appear that one adjustment will undo another, it might not be all that critical. Starting closer to the output as the manual shows might just make the subsequent adjustments more visible.
     
    Last edited: Jun 15, 2018 at 6:01 PM
  15. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,416
    Location:
    Ball Ground, GA
    You can go one way or the other -- the primary concern is to keep the signal strength low at all times, so the limiter stages don't go into limiting. If they do, you won't be able to see the effects of minute adjustments made. With a weak signal, and without test equipment, I like to start at the beginning of the IF strip because the earliest stages do the most amplification and getting them right will have the biggest impact on the unit's ability to receive the intended signal. Ideally, you would actually start with the second IF transformer, and assume that hopefully the first one is still good and untouched. That way, it can be taken as the reference of 10.7 mHz, with the rest being peaked to its setting.

    Dave
     
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  16. fred soop

    fred soop Super Member

    Messages:
    1,915
    Yep. There was a standard that was actually published someplace, possibly the Audio Cyclopedia, but I can't find it today. Sometime in the 1970s, this got reversed and today left channel is tip, right is ring. However, I cannot find a standard and also got no response from Koss, the headphone experts.

    Another problem to watch for: If you have a miniplug to dual RCA cable, the miniplug may be wired either way. (Been there, seen that). Check with an ohmmeter and mark the miniplug end with red or white tape to indicate which RCA goes to which connection on the plug.
     
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