I need help with FM Tuner alignment

Discussion in 'Tuners' started by kenwoodm2a, Aug 8, 2018.

  1. kenwoodm2a

    kenwoodm2a New Member

    Messages:
    4
    Hello Folks!

    I am looking for expert help trying to decipher some of the service manual alignment set points for my Kenwood tuners. I did take my electronic course many moons ago and have been going through some of my literature but I am still having issues in some areas as I have never done an alignment but am more than confident that I can figure it out, I'm just having a little trouble getting out of the gate!

    I have 4 Kenwood tuner/receivers that I refurbished but am now at the stage where I would like to check and align the tuner section if required. I have all 4 service manuals, volt meters, a 60 Mhz scope...Yes, I know that it's not enough for FM alignment but I have a new 200 Mhz scope on it's way and should be here Friday. I also acquired a Jung Jin JSG-1101B FM/AM Stereo Signal Generator which I believe to be a Kenwood SG-5110. Both units appear to be identical and spent last weekend familiarizing myself with it's operation. It's output can be selected at dBu EMF or dBm. And yes, I did construct an impedance matching pad so I'm good to go. I also have a distortion analyzer.

    The 4 units are....

    Kenwood Model Eleven GX..........I LOVE this unit! The sound is so crisp and has a very warm natural sound to it!

    Kenwood KT-3300d

    Kenwood KT-5020

    Kenwood KRC-939 ........Automobile Deck

    The first thing that I would like to point out is that I don't understand why the manufacturers can't keep things simple and use actual voltages instead of using dB, dBu EMF, dBm or any other forms. All this just adds to the confusion. It is my understanding that Japan manufactures used dBu EMF but none of my manuals make reference to that. I have also been using this web site for conversions...... https://www.eeweb.com/tools/rf-unit-converter ......but without knowing for sure what they are actually using in the service manual, it complicates things a little.

    My vintage Model Eleven GX from the late 70's uses dB (ANT INPUT) and makes reference in the manual that 0 dB = 1 uV.

    My KT-3300d and KT-5020 from the late 80's both use dBu (ANT INPUT) with no reference.

    My KRC-939 from the late 80's uses dB (ANT INPUT) with no reference.

    As you can see, there is no consistency from one unit to the next as far as input levels go which is confusing.
    So now let's move on to the actual alignment. This will be for the KRC-939. I have a spare unit that I marked all the pots with a fine tip marker so that I can go back in the event I screw up. I'm using this deck as a practice unit.

    The first adjustment is discriminator.... input setting 98.1 Mhz, 0 dev, 60dB (ANT INPUT)......output setting DC volt meter across TP6........Tuner setting 98.1 Mhz and align T3 for 0 volt.
    I had no problem getting this completed and it was very close already.

    The next adjustment is Stop Level..... input setting 98.1 Mhz, 0 dev, 20dB (ANT INPUT) .....no output setting, was left blank.......Tuner setting 98.1 Mhz and adjust VR6 for Stop.

    What the hell is Stop Level? I tried adjusting this pot but did not see anything change on anything.

    My KT-5020 also has this alignment and says align .......To the position so that the lowest level of the S meter lights.

    Next adjustment is Distortion.........input setting 98.1 Mhz, 75khz dev, 60 dB (ANT INPUT).........no output setting, was left blank.......Tuner Setting 98.1 Mhz and adjust VR9 for minimum distortion.

    How am I suppose to read the distortion level? My service manual makes no metion of a distortion meter, only a volt meter and a scope on the output across speaker.

    Next adjustment is Pilot Canceler........input setting 98.1 Mhz, 0 dev, Pilot : On, 60 dB (ANT INPUT)........Output Setting is Volt Meter and Scope.......Tuner setting 98.1 Mhz and adjust VR10 for minimum output.

    Once again, I could not see any change on the scope as I adjusted this pot. Of course I was using my 60 Mhz scope and perhaps I need to try again with my new 200 Mhz scope once it arrives on Friday

    Next adjustment is Separation.........input setting 98.1 Mhz, 1Khz +or- 68.25 Khz dev , Selector L or R, Pilot : +or- 6.75 Khz dev, 60 dB (ANT INPUT).......output setting is Volt meter and Scope.........tuner setting is 98.1 Mhz and adjust VR11 for minimum crosstalk.

    I'm not sure about the Pilot : +or- 6.75 Khz dev part as far as setting my generator for this.

    There are a couple more adjustments that need to be checked but we can start with this as I believe that once I figure these out with some help, the rest will all fall into place, at least I hope!
    I really hope that once I get my new scope that I will be able to see what I'm suppose to be looking for cause right now I have no idea what the output is suppose to look like.

    If there are any experienced tuner experts here, then I would be very grateful for any help that I can get!

    Thanks!
    Roland
     

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  2. Punker X

    Punker X Moderator Moderator Subscriber

    Messages:
    3,955
    Location:
    Panic in Detroit
    Not sure on your KRC, would have to look at the schematic to figure out what the circuit is doing. Maybe someone else has experience with this.

    On the 5020, you are measuring the THD of the audio from the output RCA's.

    Pilot canceler to see a difference you will have the lower the vertical voltage down so you see grass. You are looking for 19Khz artifacts from the MPX process. Adjusting you will see a change in the level of the grass. Adjust for the lowest level and even between left and right.

    For the separation. Don't have time this morning to look up your manual, but there should be a way to adjust the pilot level. Might be a shift button and the Pilot on/off. Usually adjustable from 0 to 10%. The deviation is the modulation level on FM. 100% would be 75khz. Should be able to adjust the level in the modulation section of the generator.
     
  3. kenwoodm2a

    kenwoodm2a New Member

    Messages:
    4
    Thank for the reply!

    On the 5020 as well as all my tuners, I do realize that distortion is measured at the RCA outputs. The manuals just simply make no reference to using a distortion meter so I assumed that I was suppose to measure it with a scope or volt meter.
    I guess I'm suppose to feed a signal from my distortion meter output to the external input of my generator then feed the output of the tuner back into the input of the distortion meter in order to analyze the signal?

    Yes, I can adjust the pilot level from 0 to 15 % on my generator.
     
  4. rcs16

    rcs16 Super Member

    Messages:
    3,720
    Location:
    Baldwin, Ontario, Canada
    yes
    turn pilot on to test stereo decoder and if you are providing the sub-carrier modulated signals to do stereo separation and thd adjustments. Most tuners, you adjust thd in the detector with a mono signal.
     
  5. kenwoodm2a

    kenwoodm2a New Member

    Messages:
    4

    So what kind of signal should I use to detect THD? I was not aware that I had to feed a signal from my distortion meter into the tuner and then check the output from the distortion meter.........Is this how all distortion meter/analyzers work? Are there distortion meters that just analyze the output without having to feed its own input?
     
  6. rcs16

    rcs16 Super Member

    Messages:
    3,720
    Location:
    Baldwin, Ontario, Canada
    use a pure sine wave to modulate the FM generator. measure the received sine wave for thd
    a D/A is just that, it does not need to have an oscillator, but most audio test sets have both a sine wave osc and a D/A to make them complete.
     

     

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  7. kenwoodm2a

    kenwoodm2a New Member

    Messages:
    4
    I had some good luck today!
    Played around with my distortion meter and my new scope. After several hours of getting to know both of these units, I was finally able to figure out how to check and adjust my distortion level. The tuner was actually close but was able to tweak it a little better.
    My Amber distortion meter works like a charm and has some really nice features and some awesome specs!. Was well worth the money, although I did not spend much for it!
    Now I just need to pick up some extra bnc cables and continue experimenting till I can do this with my eyes closed!
     
  8. rcs16

    rcs16 Super Member

    Messages:
    3,720
    Location:
    Baldwin, Ontario, Canada
    Nice to hear you figured it out and you like your Amber, I like my 3501 as well.
    One thing to watch is the blue ITT tantalum caps short out over time, sometimes catastrophic. I have had to change 2 of them so far and there are many inside this unit.

    I have bought some cables/adapters this year from a seller on ebay, the prices are hard to beat but free delivery can take some time, up to a month.
    the seller was xqv3000 (https://www.ebay.ca/str/rfconnectorstore)
    if you want hi quality RF stuff, go to https://www.pasternack.com/
     

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