Help with fm tuner

[globo2006]

Wow. How much information to analyze !!! I'll start reviewing what they suggest. Thank you very much to all

Meanwhile I tell you that today I was doing some tests and I can tell you the following:

1- Measure conductivity between the FM meter and the switch function and is correct. That is to say between the meter and the points 53 and 54 of the graph that I attached and of them to the terminals of the switch. All ok

2- I also measured conductivity between point 59 and the lamp indicating stereo and was fine. Another thing I did was measure conductivity between lamp terminals and had, so I guess the lamp is not burned.

3. After I was trying other things. I put FM function and medi conductivity between the points from 1 to 15 (see attached) and all were connected to each other. I did the same between 16 and 30, in that case they were only connected between the 22 and 25

4- Then followed with the connectors facing, eg 1 and 30; 2 and 29, and so on. Always on FM function. Those who were connected were: 10-21; 9-22; 6-25.

5- Then change function to Phono and aux and all facing pairs had connectivity (?????) ie 10-21; 9-22; 8-23; 7-24; 6-25

6- Then go to review the variable capacitor and there I find fault. The dial cord pulley shaft has play (important) in the direction indicated in the attachment. This axis in turn has a pinion that gives movement to the solidary crown with the variable capacitor. And it happens that when I want to make a fine tuning of a certain frequency I will not allow it. Since you want to return a few millimeters back or forward, the needle moves a lot until you find the desired station again. This will have to be solved before proceeding with another topic

7- Finally found a capacitor (c313) in poor condition. I was losing liquids.

 

[I LIKE MUSIC]

rcs16, exactly. I described TP1 and circled it in the second picture in my post, it is what he will need to use to tweaking the FM front end and the output of the mixer.

globo2006, it appears that you are making progress. What I would like to see is getting enough signal/sensitivity to have it operate with the muting turned on (stereo mode). The stereo light just might work in this case, although we do not know for sure.

 

[globo2006]

The truth is that I am very happy with the progress I am having and all thanks to his advice.
I think I'll find the solution. I will try the weekend to start calibar the TC1 and TC2, as well as try with the multimeter the voltage in TP1

 

[globo2006]

Today I dedicate myself to repair the axis of the variable capacitor I had mentioned in previous posts. Also replace the capacitor you had exploded.
I did not have more time to do the tasks that I recommended rcs16 and I Like music, but as if to go forward something I arranged to mark the position of the screws of the capacitors TC1 and TC2. It was very big surprise when I saw that they were fully adjusted, ie they are as if someone with a screwdriver would have adjusted to the maximum.
So I think I will have a hard job until I find the right position.

 

[I LIKE MUSIC]

Good luck with the tuning capacitor repair.

If the trimmer capacitors are misadjusted that will reduce the sensitivity of the tuner. There may be other things misadjusted.

Keep us up to date.

 

[globo2006]

Thank you Like a Music. I'll keep you informed

 

[larryderouin]

globo; The slack (sloppiness) in the Variable capacitor gear train is a common problem in the lower ended x80 series. About the only thing you can or should do is just learn to live with the sloppiness and adjust slowly and very small increments. Learn to tell when the slack is taken up and then when the cap moves. If you can find a 680-780 with a tight gear train, swap it out. It has to be just right (the intermediate gear with the spring) or it won't work right.

FM MUTE; This monitors FM input signal level and blanks out interstation hiss and signals that are less than the threshold level. When it's off it allows all input signals and noise/hiss. Unfortunately in the PIONEERS it is not adjustable, like in some Sansui's (good feature). This is why when you have it ON, you get almost no sound from anything on FM due to most all of the signals being below the threashold level. In areas where you have a lot of stations and you listen to only 2-3 of them, leave it on so you don't have to hear all the Hash. When you want to listen to a weaker station it's best to leave it off so you can tweak the tuning a bit more than with it off. Usually when the stereo lamp goes off, the Muting kicks in. At least that's my experince with PIONEER's.

FM is line of sight, vs AM which skips off the ionosphere and goes great distances over the Horizon, especially at night. Range on FM radio is normally 30-40 miles (48-74Km) for good reception and 50-60 miles (92.6-100Km) for what's called Fringe reception on flat terrain with no tall bldg's between you and the tower.. Fringe area is where the Mono signal is fading out. Stereo signal needs 3-4 times more signal power than a Mono signal. So if you are 20-40 miles away from the FM TOWER, depending on the transmitters power in kW, your antenna height and aiming, and the alignment of your tuner, you may or may not be able to get a Stereo Signal, even if the MONO Signal is fine. Couple things you can do is to get an outdoor antenna strictly for FM reception (a yagi is highly directional so a rotator on the pole is usually required.) Look up the distance from your house/apartment/condo to the radio station's transmitter antenna, and look for any tall hills, skyscrapers, between you and the tower. There is a phenomenon called FM Multipath that can screw up your reception and actually cause distortion. Tweaking the antenna's direction slightly can reduce or alleviate the problem in most cases. If you live in a Large city with tall bldgs around you with steel frames and/or siding, Multipath becomes a real problem. The only way to get rid of it is to make sure your antenna is higher than the surrounding bldgs.

Some light General knowledge reading; Google: 1.) FM Multipath 2.) FM Stereo Reception and distance. 3. Stereo vs. mono FM Reception. Then search the stations you listen to, and get the coordinates for the transmitter tower, and your place. Then google a topographic map of your area and look for hills higher than the top of the antenna tower, between you and the tower.

If you own your house, install a roof antenna (if you are far away from the transmitter). How high above the roof is dependent on you. If you live in an apartment bldg check with the owner and see if he'll allow you to mount an antenna on a 8ft pole(use a rotator if needed on both). If you get good to very good reception on a dipole antenna, mount it in the attic (if you have one) or on the roof on a wood frame. it can lay on the roof flat. Make sure the antenna legs are stretched out full length and are perpendicular to the direction of the transmitter (this in all cases). In other words if the station transmitter is to the EAST, orient the legs North-South.


Good luck with it. Looks like you are getting some good help.

Larry

 

[globo2006]

Thank you Larry very good recommendations.
With respect to the antenna, I have other tuners in my house (digital) and with a simple cable tune all the stations of my count

With respect to the variable capacitor shaft clearance I have been able to repair it but I realize that it may happen againry.
That's why I'm trying to see what happens with the 680 because I also know that their tuners were very good

Thanks again

 

[larryderouin]

As long as you don't try to spin it across the dial in one shot it should last a long while. Digital tuners are a fair amount different than Analog tuners. They lock on the exact frequency, where with an analog you might be off .1mhz at the peak.

 

[globo2006]

Following the advice of I LIKE MUSIC, P tuning TC1 and TC2 and managed to tune and listen properly the FM stations in my area but as I was still not working the tuning meter and did not turn on the indicator light of stereo.
So with a multimeter make the measurements that I recommend I LIKE MUSIC


I also measured directly at the input terminals to the tuning meter and the values were the same

The results were the following:
The measurement at the ends of the 300 ohm resistor never showed negative values, it oscillated about 19 and 20 volt but always positive. I never tended to zero

Then, as indicated in the following figure, measured the voltage between TP1 and ground and the value was about 1.95 volts


Connect a battery to the stereo indicator lamp and the same light. I did this to rule out that I was burned

Below I show two images of the tuning meter. The first is when I tune in well to a station and the second when I do not




It is undoubted that the signal that is reaching the meter to always be of a positive value does not bring the needle to the center. The question is what is causing this failure?

 

[rcs16]

It can only be a couple of things, it has nothing to do with the FM front end. You could disconnect the FM front end, ground the IF input, it will do the exact same thing, being that the tuning meter is off to the side. It is the quadature detector circuit having a problem. The circuit is a phase detector that relies on the out board components to tune to the IF freq at 10.7Mhz and phase shift it the correct amount to have a zero AFC vs the ref bias pin. There is a reference bias pin 10, it is a fixed voltage and the AFC pin 7 deviates +/- from that reference voltage. This also is part of the deviation muting circuit as the R between the ref bias and the quad IF o/p sets the freq deviation muting threshold. The DCV on the audio out, pin 6 basically does the same.
Change the discriminator IC, and if that does not work then the quad coil, series inductor are out of spec.
We are having the exact same problem on a sx-1980 that using the same components. Those PAxxxx chips are dying out these days. Could try a HA11225 if you can not locate the PA3001A, which are hard to find. A real PITA

 

[I LIKE MUSIC]

rcs16, I have been through this in a private conversation with the OP. It appears that there is not enough adjustment range to center the tuning meter.

The reason for tweaking the RF front end is because the FM muting cuts out all reception. Just a starting point to take that out of the equation since it is so simple to do.

And yes there have been several receivers using basically the same circuit that have had failures of the ICs, the ceramic filters, ceramic capacitors, resistors and so on along with the FM detector transformer. Even an RF transistor or two failure.

 

[globo2006]

These are the measured values

Pa 3001-A
1- 2.03 v
2- 2.04 v
3- 2.04
4 y 5- 0 v
6- 7.5 v
7- 5.7 v
8- 5.7 v
9- 5.7 v
10- 5.7
11- 12.93 v
12- 3.8 v
13- 1.9 v
14- 0 v
15- 4.8
16- 4.1 v

PA 1001-A
1- 12.75
2- 2.98
3- 5.28
4- 8.32
5- 8.32
6- 7.46
7- 0
8- 3.45
9- 0.8
10- 2.43
11- 2.39
12- 2.51
13- 2.51
14- 2.54
15- 3.62
16- 0.69

 

[I LIKE MUSIC]

It is best if you just keep one thread going, it can be difficult to follow two threads about the same thing.