Any Scott 433 nixi tuner owners?

Discussion in 'Tuners' started by CJVx, Dec 29, 2017.

  1. CJVx

    CJVx AK Subscriber Subscriber

    Messages:
    153
    Location:
    NJ
    IMG_7352.JPG Hello, I am working on mine, would like to know if anyone has any pictures of the inner working to help me resolve an inconsistency. This section looks wrong and differs from the schematic. Problem I have is it won't lock on a station nor tune in stereo. This resistor matrix has a part in both of those functions, but I think it's wrong. Thanks!
     

     

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  2. txturbo

    txturbo Well-Known Member

    Messages:
    865
    Location:
    Austin, TX
    Can you share the schematic and describe the problem in greater detail?

    Looks like an interesting tuner!
     
  3. CJVx

    CJVx AK Subscriber Subscriber

    Messages:
    153
    Location:
    NJ
    Hello, unfortunately I don't have a digital copy of the schematic, had to purchase the paper copy. But I will show the section in question, the picture of the block diagram shows the resistor networks above the highlights. I did rebuild this section as per the schematic, but the problems I have persist, which are no perfectune indicator and no stereo. Because of these problems, the tuner will continuously scwn and not stop on stations or stereo stations, although it can be manually tuned in and sound good in mono. I'm pretty sure the op amp IC in the perfectune circuit is dead, so I am attempting to rewire an IC socket to except what I think will be a compatible but obtainable op amp, but that is yet to be determined. I am going to pick up an NTE857 and Match the inputs, output, and rails as shown in the schematic, and what I'm assuming is that pins five and six in the schematic will be the nulls on the NTE857.
     

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  4. txturbo

    txturbo Well-Known Member

    Messages:
    865
    Location:
    Austin, TX
    As a test I would try and simulate the opamp changing states and see if that gets the stereo lamp working..

    1) Tune to a known station manually.
    2) Measure the voltage at pin 6 of the perfecttune PCB. I think it should be at the rail voltage of the opamp when the perfecttune lamp is off, ground when it's on.
    3) Disconnect the wire from pin 6 and ground the wire.
    4) The perfect tune lamp should come on and this may effect the stereo multiplexer, allowing it to go into stereo. It looks like pin 2 of the mux circuit needs to see the perfect tune lamp on.

    I can't really read the big schematic, the resolution of the image is too low, can you post a better image?
    Can you post a schematic of the multiplex section?
    Do you have the alignment procedure?
    What do you measure at pins 1, 4 and 5 of the perfect tune PCB when a signal is centered and strong?
    Is there a functional description of the circuit in the service manual?
     
  5. CJVx

    CJVx AK Subscriber Subscriber

    Messages:
    153
    Location:
    NJ
    Thank you so much for your help and tips, I am making pretty good progress here, see my answers in your quote and I attached a scan of the multiplex

    What I did find out was that the MUX was way out of alignment, so using a method I have used before with success, I managed to get the stereo lamp to come on on it's own and got really good separation and no distortion. Only issue though, is I have the stereo threshold pot set the minimum, or else it will never snap into stereo. Also most of the time, if I were to push the mono button And then release it the stereo light won't come on again until I turn back into the station. So something must be weak here, but I am using the incorrect voltage stereo indicator lamp lamp, so I'm not going to sweat this until I install the proper 24 V lamp that I have on order. Things are looking up which is good, and the sound quality out of this tuner is phenomenal.
     

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    Last edited: Jan 11, 2018

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