I need help with FM Tuner alignment

[kenwoodm2a]

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

 

[Punker X]

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.

 

[kenwoodm2a]

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.

 

[rcs16]

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
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.

 

[kenwoodm2a]

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.

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?

 

[rcs16]

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.

 

[kenwoodm2a]

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!

 

[rcs16]

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/

 

[Bob@FM]

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!

So please beware, depending on the tuner output filtering, the 19 kHz pilot may show up as distortion when doing measurements with an old school analog distortion meter.

 

[kenwoodm2a]

So please beware, depending on the tuner output filtering, the 19 kHz pilot may show up as distortion when doing measurements with an old school analog distortion meter.

You might be right as you guys are far more knowledgeable in this area than I.
The pot that I adjusted was specific to distortion according to service manual but I most certainly will keep that in mind when I check the pilot alignment to see if the results are the same.
Thanks for that info, it all helps me!

 

[Bob@FM]

You might be right as you guys are far more knowledgeable in this area than I.
The pot that I adjusted was specific to distortion according to service manual but I most certainly will keep that in mind when I check the pilot alignment to see if the results are the same.
Thanks for that info, it all helps me!

You'll be fine if you keep the stereo generator pilot OFF when measuring THD. If you turn it on, and repeat the THD measurement, you'll likely see a big increase in distortion. On some/most distortion sets you can tune to the 1 kHz signal created by the stereo generator. If you want to use the generator in the distortion meter (usually it's better) make sure to get the level correct. Use a scope, and adjust it to match the audio level out of the tuner when using the internal stereo generator sine wave.
I use an FFT display to do all my distortion, pilot cancel, and separation adjustments. In that case you can see the individual frequencies, like 1 kHz and harmonics, or 19 kHz (to minimize).
Bob

 

[kenwoodm2a]

You'll be fine if you keep the stereo generator pilot OFF when measuring THD. If you turn it on, and repeat the THD measurement, you'll likely see a big increase in distortion. On some/most distortion sets you can tune to the 1 kHz signal created by the stereo generator. If you want to use the generator in the distortion meter (usually it's better) make sure to get the level correct. Use a scope, and adjust it to match the audio level out of the tuner when using the internal stereo generator sine wave.
I use an FFT display to do all my distortion, pilot cancel, and separation adjustments. In that case you can see the individual frequencies, like 1 kHz and harmonics, or 19 kHz (to minimize).
Bob

Thanks again Bob!
I just realized after reading your post that I did have the Pilot OFF when I made my distortion adjustment. I had carefully marked the pot with a fine tip maker and I could see the distortion increase and decrease on both my scope and distortion meter when making the adjustment. The factory setting was very close and I hardly had to move the pot much.

 

[kenwoodm2a]

I also discovered another issue when following the service manual adjustment procedure.
The manual says to set my generator for 98.1 Mhz and set tuner for 98.1 Mhz for most of the procedures.
What am I suppose to do if I have a strong station at 98.2 Mhz spilling over, affecting my readings?
Is there a reason why it has to be 98.1Mhz? Can I set my generator for 97.7 and set tuner for the same and do my adjustments at that frequency?

 

[Punker X]

Is there a reason why it has to be 98.1Mhz

Its in the middle of the scale. You are good moving down to 97.7.

 

[kenwoodm2a]

So here were the first 3 steps for aligning the FM section in my deck..........

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.


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.


I did manage to get these done.........so far so good!


Not so simple for the following 2 steps

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. I tried every thing I could but yet could not see anything change on my scope. The service manual says to use a scope and/or AC voltmeter at the audio output. Do I need to build myself a 19 Khz trap so that I can isolate that frequency on my scope?
I finally used the line level input of my distortion meter with the low pass 30 Khz filter and tuned the pot to give me the lowest reading. That reading was pretty much factory set. I'm not sure if this is the way to go. Can anybody show me what the pattern on my scope should look like doing this alignment?

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 connected the scope and AC meter to the audio output as indicated in the service manual and was able to get a reading on my meter as I adjusted the pot. As I turned it one way, the level would drop and the other way the level would increase but it stopped increasing once I hit the factory setting that I had marked with a Sharpie before making the changes. So I assume that we want the higher level here and not the lowest?
What does crosstalk look like on a scope?


I don't come close of having the knowledge that you folks have with tuner alignments and how to interpret what I see on my scope. Once I get the first time, then I'll be good to go as I document everything so I don't forget.

Any extra help would be grateful !

Roland

 

[Punker X]

Where did you have your Volt/Div setting on the scope when you did the Pilot canceler adjustment? To see the pilot you have to turn it down. It will pretty much look like grass.

When doing the separation, modulate left or right on the scope, if perfect you will have a sine wave and a flat line. If the flat line is not flat, that is cross talk. You want to adjust so it is as flat as can be. Change between Left and Right so it is even and not out of balance. Again you will need to decrease the Volts/Div to see the cross talk. If you have it set to see the nice sine wave you may not see any crosstalk.

 

[kenwoodm2a]

Where did you have your Volt/Div setting on the scope when you did the Pilot canceler adjustment? To see the pilot you have to turn it down. It will pretty much look like grass.

When doing the separation, modulate left or right on the scope, if perfect you will have a sine wave and a flat line. If the flat line is not flat, that is cross talk. You want to adjust so it is as flat as can be. Change between Left and Right so it is even and not out of balance. Again you will need to decrease the Volts/Div to see the cross talk. If you have it set to see the nice sine wave you may not see any crosstalk.

Thanks for you input!

I had it turned down to see grass but still no luck. I have tried everything to see that pilot signal even looking at the scope while I turn the pilot on and off to see if I could see a change in the pattern but no way. I must be doing something wrong.
I finally tried using my distortion meter and feeding to the line level input and turning the low pass 30 khz filter on. I was able to watch the needle indicator increase and decrease as I adjusted the pot and set it for the lowest level which was almost exactly where the factory setting was so I figure that must be correct. The needle even dropped to zero when I shut the pilot tone off so I'm guessing it must be correct.

As far as the cross talk goes, I did figure that out by using to ac meters on the audio output and switching from left and right on the generator and adjusting the pot so that I had zero on on channel and max on the other and then switched to the other channel and did the same. I was able to get it right and once again the pot was almost exactly at factory setting. I mark all my pots with a Sharpie before making changes.

I just wish I could see that damn 19 khz signal on my scope!

thanks again!
Roland

 

[ConradH]

Don't know the tuners, but there's usually a test point for the 19 kHz signal trap. Remember that every alignment procedure ever written seems to have errors and omissions. The only place you need a filter is when making THD measurements. Simplest one is a passive notch filter you can build in a little BNC-BNC box from Pomona. On your original comment about volts, the RF world just doesn't find those convenient. Most everything will be log voltage or log power into a defined impedance. Keep those converters handy!

 

[Punker X]

You do have the pilot turned on your signal generator? Should be on. Stereo lamp should be lit.

 

[kenwoodm2a]

You do have the pilot turned on your signal generator? Should be on. Stereo lamp should be lit.

Yup! Sure do! Both pilot and stereo are lit.
I tried shutting off the pilot to see if there was a difference on the scope display but did not see any. I did at one point connect a probe to a leg on the pot and was able to see a difference on the scope when I adjusted the pot and it was correct with the factory setpoint. However, I have not been able to recreate it no matter what I tried. Perhaps things will be easier when I try doing the alignment on the KT-3300d instead of this car deck that I'm practicing on.