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I need help with FM Tuner alignment
I need help with FM Tuner alignment
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Old 25th August 2018, 11:16 PM   #21
KenwoodM2A is offline KenwoodM2A  Canada
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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
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Old 25th August 2018, 11:36 PM   #22
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by KenwoodM2A View Post
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?
The intention is that you look at the silent output, is that what you do? For example, modulate left and measure right. The level at the silent output should be as low as possible.
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Old 25th August 2018, 11:40 PM   #23
Bill_P is offline Bill_P  United States
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The pilot tone should just be a tiny 19 kHz sine wave at the tuner audio output. It should not be necessary to build an external circuit to aid the scope. If the scope does not have the sensitivity to view the pilot tone then it isn't up to the task. Your distortion meter may be a better tool for this adjustment. Adjust VR10 for minimum output on the distortion meter. Then shut off the pilot tone on the FM generator. Does the distortion meter reading drop? Ideally it should be near zero. If so, then you are in fact reading the pilot tone on the distortion meter and the adjustment has been successfully completed.

Separation is checking alternate channel leakage. Set the FM generator to 1 kHz 68.25 kHz deviation for the left channel only. Measure the tuner right channel output and adjust for minimum 1 kHz output. Repeat with generator tone set to right channel and measure the tuner left channel. Adjust so that there is balance in the minimum output for the both channels. That is, driving the left and then driving the right channels should produce similar output amplitude.
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Old 26th August 2018, 04:06 AM   #24
KenwoodM2A is offline KenwoodM2A  Canada
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Quote:
Originally Posted by MarcelvdG View Post
The intention is that you look at the silent output, is that what you do? For example, modulate left and measure right. The level at the silent output should be as low as possible.


Got it, thanks!
I used both of my ac meters hooked up to each channel and switched from left to right and was able to get it!
I took notes so now I know what to do the next time.

Thanks again for input!
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Old 26th August 2018, 04:24 AM   #25
KenwoodM2A is offline KenwoodM2A  Canada
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Quote:
Originally Posted by Bill_P View Post
The pilot tone should just be a tiny 19 kHz sine wave at the tuner audio output. It should not be necessary to build an external circuit to aid the scope. If the scope does not have the sensitivity to view the pilot tone then it isn't up to the task. Your distortion meter may be a better tool for this adjustment. Adjust VR10 for minimum output on the distortion meter. Then shut off the pilot tone on the FM generator. Does the distortion meter reading drop? Ideally it should be near zero. If so, then you are in fact reading the pilot tone on the distortion meter and the adjustment has been successfully completed.

Separation is checking alternate channel leakage. Set the FM generator to 1 kHz 68.25 kHz deviation for the left channel only. Measure the tuner right channel output and adjust for minimum 1 kHz output. Repeat with generator tone set to right channel and measure the tuner left channel. Adjust so that there is balance in the minimum output for the both channels. That is, driving the left and then driving the right channels should produce similar output amplitude.
I have no idea why I'm having such a hard time picking up that 19 Khz pilot tone. My 200Mhz scope is brand new and I even tried with my older 60 Mhz scope with the same results.
You are correct about the distortion meter that when I turn the pilot on the generator off, the distortion meter level does in fact drop off to zero so I think that with the low pass 30Khz filter on the distortion meter, I'm actually able to minimizing the 19 Khz tone.
I just wish I could see it on the scope.

As far as the separation goes, I managed to get it as I mentioned in the previous post.
I adjusted so that there was an equal balance between both channels.
Actually, I was able to get zero on both channels when switching back in forth with an equal amplitude on the opposite.

Now on to the AM section.......I know, why would I waste my time?
Just for fun!
Plus this tuner has C-QUAM Stereo AM and I have a C-QUAM AM transmiter so it will give me a chance to play around.
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Old 27th August 2018, 01:19 AM   #26
PRR is offline PRR  United States
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The 19KHz rejection is critical if you are going to put the tuner signal to tape. It can beat against the tape HF bias and cause birdies.

Because tape is going out of style, this may be moot.

Because all this stuff is going out of style, yet you still play with it, you may have tape also. Record tuner output, playback, and listen for steady tones which should not be there. Note that some cassette decks also have 19KHz filters.
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Old 28th August 2018, 02:31 AM   #27
KenwoodM2A is offline KenwoodM2A  Canada
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Quote:
Originally Posted by PRR View Post
The 19KHz rejection is critical if you are going to put the tuner signal to tape. It can beat against the tape HF bias and cause birdies.

Because tape is going out of style, this may be moot.

Because all this stuff is going out of style, yet you still play with it, you may have tape also. Record tuner output, playback, and listen for steady tones which should not be there. Note that some cassette decks also have 19KHz filters.

Yeah, I won't be making any radio recordings.
I do have a couple high end tape decks that I restored but not for that purpose. I also have a vintage reel to reel that I restored but that was just to add to my little collection.
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Old 28th August 2018, 03:03 AM   #28
KenwoodM2A is offline KenwoodM2A  Canada
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So I just remembered something I need to check on.
The tuner that I'm practicing my alignments on is a spare Kenwood KRC-939 car deck. This model was probably the best car deck Kenwood ever made and the price tag of $1100 back in 1988 might very well justify it. The only other model that was more expensive was the KRC-999 and only cause it had a motorized EQ door that slid out from the unit. Other than that it's the same unit and transport. I bought it new and have completly restored it and recapped the entire unit.
So here is the question that I have.
The service manual indicates what settings to turn on or off for the tuner and alignment procedure which I did.
What it did not indicate is volume level. The deck has two pre outs. I connected my scope to the audio outs and turned the volume up so I could get a reading on my meters and scope. The service manual shows the output settings with a picture of the deck with the output RCA's then a speaker, then the probes of the meter and scope at the speaker.
Does this indicate that I need to place an 8 ohm load on the output and measure across the load?
Now here's an even more important question....if I turn the volume up on the deck without a load on the RCA outputs, will I blow and fry the preamp stage???
I was always under the impression that you can harm the output stage without a load on it.

Last edited by KenwoodM2A; 28th August 2018 at 03:24 AM.
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Old 28th August 2018, 04:23 AM   #29
PRR is offline PRR  United States
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> will I blow and fry the preamp stage???

No.

Even idiots design line-outs that are not harmed by no-load.

99% of transistor power amps (99.99% of car power amps) are fine no-load.

The "killer" is *tube* power amps when OVER-driven. The sharp cut-offs make the output transformer kick-back, to possibly 10X the B+. A minute of this will punch-through insulation.
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Old 29th August 2018, 02:22 AM   #30
KenwoodM2A is offline KenwoodM2A  Canada
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Quote:
Originally Posted by PRR View Post
> will I blow and fry the preamp stage???

No.

Even idiots design line-outs that are not harmed by no-load.

99% of transistor power amps (99.99% of car power amps) are fine no-load.

The "killer" is *tube* power amps when OVER-driven. The sharp cut-offs make the output transformer kick-back, to possibly 10X the B+. A minute of this will punch-through insulation.

Thanks for that info.....
I had a feeling that it was ok but I just wanted to confirm that.
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