Pioneer FM Tuner Alignment

jim249

Active Member
Hi All; I have a few older Pioneer Receivers that have been laying around for years now with the FM tuners that are out. Some are better than the others. Is there a simple procedure out there for tweeking the front end? I have read of one for a Marantz where you adjust the LO, RF, IF coils. I only paid a buck or two for these receivers so am not concerned about what happens to them. I am just looking for a simple wing-it procedure to tweek these receivers. Thanks for any help.

I do have the plastic alignment tools for this project.
 
I have used the following simple procedure for many years and it has served me well. I do this on all of my vintage solid state receivers, as the front ends are all usually very similar.
Before performing any alignments, make sure that the FM front end is securly screwed to the chassis, and that there aren't any cold solder joints where the front end connects to a circuit board, either connections from the metal frame of the tuning cap, or the individual connections from the plates.
Check also for a scratch sound when tuning up and down with the FM muting off. If you can hear a scratching sound, you need to put a very small drop of oil
on all of the points where the brass shaft meets and touches the copper spring guides. I use a deoxit fader lube pinpoint oiler for this.
I will follow up Sunday Afternoon with all the detail as well as pictures which will be helpful.
 
Do not use oil or any cleaner that will leave residue. Locate and clean the FM Oscillator trimmer that is usually located on top of the tuning gang. Work and return to original position. You can use this trimmer to adjust the dial pointer. Cleaning the rest of the trimmers atop of the gang sometimes helps. Clean the FM Muting trimmer as well to make sure it is not rejecting all signal. And make sure the front panel selector switch and FM Muting switch are clean.
 
Given that various generations of "vintage" Pioneer receivers used multiple types of circuits it will be important to define what units are involved. For example, the X3X and X5X series may have used one arrangement with different type detectors/discriminators, while the X80 series may have used a completely different arrangement.
 
Given that various generations of "vintage" Pioneer receivers used multiple types of circuits it will be important to define what units are involved. For example, the X3X and X5X series may have used one arrangement with different type detectors/discriminators, while the X80 series may have used a completely different arrangement.
The models are Pioneer 525, 750, 780 and Marantz 2218, 2225, and a Sansui 4000.
 
I cannot address the Marantz units. However, the Sansui 4000 is a larger variant of the 3000 within which I've been intimately involved in the tuner section. The 3000 used some germanium transistors which complicates it a bit. I am unsure of the 4000 also uses Ge devices, but the tuner uses a full discrete component ratio detector type circuit with OP amps and adjustable inductors. This allows for COMPLETE alignment of just about every stage of detection and separation.

The SX-750 uses a combination of ICs and discrete devices along with ceramic filters in the IF stages, allowing for limited but decent alignment is the filters are intact.

The SX-780 is similar to the 750 but has non-adjustable inductors in the front end so tracking/linearity adjustment is a real hassle. It is imperative that the tuner variable capacitor assembly is completely cleaned and lubricated properly on this type to avoid unnecessary adjustment of the VC plate gaps. The rest of the alignment is pretty straightforward and similar to the 750.
 
Let's start with just ONE unit as our focus, and begin with a full description of the tuner operation.

Does the AM and/or FM receive at all? If so, are all stations weak or strong? Do stations with a known frequency display at the correct indicated points on the dial? At both ends?

Does the tuning meter function properly? If not, how is it acting? What about a signal strength meter?

Does the STEREO indicator operate?

Is there unusual noise? Does the MUTE function operate to suppress interstation noise?

What type of antenna is attached?
 
I have used the following simple procedure for many years and it has served me well. I do this on all of my vintage solid state receivers, as the front ends are all usually very similar.
Before performing any alignments, make sure that the FM front end is securly screwed to the chassis, and that there aren't any cold solder joints where the front end connects to a circuit board, either connections from the metal frame of the tuning cap, or the individual connections from the plates.
Check also for a scratch sound when tuning up and down with the FM muting off. If you can hear a scratching sound, you need to put a very small drop of oil
on all of the points where the brass shaft meets and touches the copper spring guides. I use a deoxit fader lube pinpoint oiler for this.
I will follow up Sunday Afternoon with all the detail as well as pictures which will be helpful.
Here is a follow-up from yesterday. Including Pictures. While there are various differences in the front ends, many are similar and easy to follow using these directions. I am also going to give you the basics for "Analog" Tuners. The adjustment for tuners without the large tuning capacitor and pulley are totally different. And only do these adjustment with units that have at least a working tuning meter, and preferrably units that also have a center tune meter or indicator, and use a pair of headphones to listen during the tuning process.
1) The FM adjustments that you should do are the ones in line with the tuning capacitor plates that have a wider spread. The sections with the closer spaced, and more plates are the AM section, which have their own adjustments.

2) Adjustments need to be made with the right alignment tool. Do not use a metal tool for the screw (Capacitor) adjustments, and do not use a metal allen wrench for the coil adjustments.
3) The more high end the receiver, the more likely you will find 4 sections for FM alignment. Lower end receivers usually have 3. If it has only three, then you need to adjust starting on the side with the shaft and pully. This is the Ant section. The next section (Middle) is the RF section, and the least section (Farthest from the pulley) is the Oscillator section which when adjusting allows you to "move" the station to the left or right
4) The trimmer Capacitor for adjusting the station to match the dial indicator, is usually found on top furthest away from the pully. This adjustment you will find is a different design than the plain screws on a piece of spring metal that the other are, as a point of reference. You will notice that the screw is smaller, and needs a fairly thin blade to adjust it. At times, in certain units, you will notice that there isn't any adjustmet on top of the tuning capacitor, for the last section of widely spaced capacitor plates. These units will almost always have these adjustable trimmer caps located on the circuit board very close the that last section on the tuning capacitor. They may also have the low end oscillator adjustment located right next to the cap

As mentioned previous, here are pictures of the FM Front end, as well as the points to lube the Tuning cap bearings if you are getting noise when turning the dial. Do the lubrication with the unit unplugged. Be very careful to not get any of the lube on the tuning plates themselves, or drip down to the board below. Just apply a very small amount to wet where the contact is and then turn from low end to high end to distribute the lube. On this example you can see marking stamped on the metal. TCA is Tuning Cap Antenna, TCR is Tuning Cap "RF", TCO is Tuning Cap Oscillator. LA is the Antenna Coil Adjustment, LR is the RF Coil adjustment, LO is the Oscillator coil adjustment..There is also another Adjustable transformer relating to the FM front end called IF. I don't recommend touching this if you don't have a distortion analyzer to look for distortion. Your ears may not pick out the distortion.

Typical FM Front End - Sansui.jpg

pinpoint bearing lube 1.jpg Pinpoint Bearing Lube 2.jpg Pinpoint bearing lube 3.jpg

Now for the High End Tuning.
Power on the unit, keep it on FM stereo, and leave the FM muting on if possible. Make sure you have at least a FM dipole antenna connected to the 300 terminals on the back. Tune to a high medium strength station around 106FM. Dont use a station that is showing a strength of 5 on a scale of 5. Check if the station identifier broadcast matches to the tuning dial indicator. It it is right on or very close, I wouldn't even mess with the "Oscillator adjustments".
1) using your alignment tool start first by adjusting TCA screw adjustment until you find the peak signal strength (you probably need to go CW and then CCw to find the best spot.
2) go to the next adjustment TCR and adjust the same was as you did the Antenna screw adjustment.
3) go to the second TCR adjustment if the unit you are working on has 4 FM sections. Adjust the screw cap adjustment the same way as the others.
4) adjust the Oscillator screw adjustment only if the dial indicator is off noticably with the station playing. In reality, many time when this difference is found, it is more likely that the dial cord is stretched causing the inconsistancy. But trying to adjust dial cords can be a pain in the neck, and you always have the chance of breaking the cord and having to redo the whole cord, so I usually adjust the oscillator rather than trying to adjust the cord, or the dial indicator on the cord.
NOTE: If the unit has a center Tune meter, note that this may not be in dead center when you have peaked the signal meter. Not to worry. Make sure you tune for the signal meter, and that the station stays on, doesn't mute, and that the stereo indicator stays on.
Pictures of high end adjustments in order.

High end Ant Tune 1.jpg High End RF A Tune 2.jpg High End RF B tune 3.jpg High End Oscillator Tune 4.jpg

Now for the Low End Tuning.
Power on the unit, keep it on FM stereo, and leave the FM muting on if possible. Make sure you have at least a FM dipole antenna connected to the 300 terminals on the back. Tune to a high medium strength station around 92 FM. Dont use a station that is showing a strength of 5 on a scale of 5. Check if the station identifier broadcast matches to the tuning dial indicator. It it is right on or very close, I wouldn't even mess with the "Oscillator adjustments".
1) using your Hex Coil alignment tool start first by adjusting LA screw adjustment until you find the peak signal strength (you probably need to go CW and then CCw to find the best spot.
2) go to the next adjustment LR and adjust the same was as you did the Antenna Hex Coil adjustment.
3) go to the second LR adjustment if the unit you are working on has 4 FM sections. Adjust the Hex Coil adjustment the same way as the others.
4) adjust the Oscillator Hex Coil adjustment only if the dial indicator is off noticably with the station playing. In reality, many time when this difference is found, it is more likely that the dial cord is stretched causing the inconsistancy. But trying to adjust dial cords can be a pain in the neck, and you always have the chance of breaking the cord and having to redo the whole cord, so I usually adjust the oscillator rather than trying to adjust the cord, or the dial indicator on the cord.
NOTE: If the unit has a center Tune meter, note that this may not be in dead center when you have peaked the signal meter. Not to worry. Make sure you tune for the signal meter, and that the station stays on, doesn't mute, and that the stereo indicator stays on.
Pictures of low end adjustments to follow in next update .
 

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Here is a follow-up from yesterday. Including Pictures. While there are various differences in the front ends, many are similar and easy to follow using these directions. I am also going to give you the basics for "Analog" Tuners. The adjustment for tuners without the large tuning capacitor and pulley are totally different. And only do these adjustment with units that have at least a working tuning meter, and preferrably units that also have a center tune meter or indicator, and use a pair of headphones to listen during the tuning process.
1) The FM adjustments that you should do are the ones in line with the tuning capacitor plates that have a wider spread. The sections with the closer spaced, and more plates are the AM section, which have their own adjustments.

2) Adjustments need to be made with the right alignment tool. Do not use a metal tool for the screw (Capacitor) adjustments, and do not use a metal allen wrench for the coil adjustments.
3) The more high end the receiver, the more likely you will find 4 sections for FM alignment. Lower end receivers usually have 3. If it has only three, then you need to adjust starting on the side with the shaft and pully. This is the Ant section. The next section (Middle) is the RF section, and the least section (Farthest from the pulley) is the Oscillator section which when adjusting allows you to "move" the station to the left or right
4) The trimmer Capacitor for adjusting the station to match the dial indicator, is usually found on top furthest away from the pully. This adjustment you will find is a different design than the plain screws on a piece of spring metal that the other are, as a point of reference. You will notice that the screw is smaller, and needs a fairly thin blade to adjust it. At times, in certain units, you will notice that there isn't any adjustmet on top of the tuning capacitor, for the last section of widely spaced capacitor plates. These units will almost always have these adjustable trimmer caps located on the circuit board very close the that last section on the tuning capacitor. They may also have the low end oscillator adjustment located right next to the cap

As mentioned previous, here are pictures of the FM Front end, as well as the points to lube the Tuning cap bearings if you are getting noise when turning the dial. Do the lubrication with the unit unplugged. Be very careful to not get any of the lube on the tuning plates themselves, or drip down to the board below. Just apply a very small amount to wet where the contact is and then turn from low end to high end to distribute the lube. On this example you can see marking stamped on the metal. TCA is Tuning Cap Antenna, TCR is Tuning Cap "RF", TCO is Tuning Cap Oscillator. LA is the Antenna Coil Adjustment, LR is the RF Coil adjustment, LO is the Oscillator coil adjustment..There is also another Adjustable transformer relating to the FM front end called IF. I don't recommend touching this if you don't have a distortion analyzer to look for distortion. Your ears may not pick out the distortion.

View attachment 721130

View attachment 721131 View attachment 721132 View attachment 721133

Now for the High End Tuning.
Power on the unit, keep it on FM stereo, and leave the FM muting on if possible. Make sure you have at least a FM dipole antenna connected to the 300 terminals on the back. Tune to a high medium strength station around 106FM. Dont use a station that is showing a strength of 5 on a scale of 5. Check if the station identifier broadcast matches to the tuning dial indicator. It it is right on or very close, I wouldn't even mess with the "Oscillator adjustments".
1) using your alignment tool start first by adjusting TCA screw adjustment until you find the peak signal strength (you probably need to go CW and then CCw to find the best spot.
2) go to the next adjustment TCR and adjust the same was as you did the Antenna screw adjustment.
3) go to the second TCR adjustment if the unit you are working on has 4 FM sections. Adjust the screw cap adjustment the same way as the others.
4) adjust the Oscillator screw adjustment only if the dial indicator is off noticably with the station playing. In reality, many time when this difference is found, it is more likely that the dial cord is stretched causing the inconsistancy. But trying to adjust dial cords can be a pain in the neck, and you always have the chance of breaking the cord and having to redo the whole cord, so I usually adjust the oscillator rather than trying to adjust the cord, or the dial indicator on the cord.
NOTE: If the unit has a center Tune meter, note that this may not be in dead center when you have peaked the signal meter. Not to worry. Make sure you tune for the signal meter, and that the station stays on, doesn't mute, and that the stereo indicator stays on.
Pictures of high end adjustments in order.

View attachment 721156 View attachment 721158 View attachment 721159 View attachment 721157

Now for the Low End Tuning.
Power on the unit, keep it on FM stereo, and leave the FM muting on if possible. Make sure you have at least a FM dipole antenna connected to the 300 terminals on the back. Tune to a high medium strength station around 92 FM. Dont use a station that is showing a strength of 5 on a scale of 5. Check if the station identifier broadcast matches to the tuning dial indicator. It it is right on or very close, I wouldn't even mess with the "Oscillator adjustments".
1) using your Hex Coil alignment tool start first by adjusting LA screw adjustment until you find the peak signal strength (you probably need to go CW and then CCw to find the best spot.
2) go to the next adjustment LR and adjust the same was as you did the Antenna Hex Coil adjustment.
3) go to the second LR adjustment if the unit you are working on has 4 FM sections. Adjust the Hex Coil adjustment the same way as the others.
4) adjust the Oscillator Hex Coil adjustment only if the dial indicator is off noticably with the station playing. In reality, many time when this difference is found, it is more likely that the dial cord is stretched causing the inconsistancy. But trying to adjust dial cords can be a pain in the neck, and you always have the chance of breaking the cord and having to redo the whole cord, so I usually adjust the oscillator rather than trying to adjust the cord, or the dial indicator on the cord.
NOTE: If the unit has a center Tune meter, note that this may not be in dead center when you have peaked the signal meter. Not to worry. Make sure you tune for the signal meter, and that the station stays on, doesn't mute, and that the stereo indicator stays on.
Pictures of low end adjustments to follow in next update .

Low end adjustments pictures

Low End Ant Tune 1.jpg Low End RF A Tune 2.jpg Low End RF B Tune 3.jpg Low End Oscillator Tune 4.jpg

You should go back to the high end adjustments to see if they have gone off peak. At times you need to go back and forth a few times to get the proper peak for low end and high end.

Other differences to mention are that
1) some tuner front ends have both the tuning adjustment caps, and tuning adjustment coils incased in metal with only an access hole. Others have only the screw caps encased in metal, with no top cover for the coils, and some have both the caps and coils exposed.
2) If the unit doesn't have a signal meter, and only has a center tune meter it is a lot trickier. I only mess with them if they are bad. The way I adjust is identify the current position of an adjustment, turn until the station mutes off, that turn back the other way until the station mutes off, and finally put the adjustment screw, or hex coil adjustment at the midpoint between the CW shutoff, and the CCW shutoff.
3) if you have it tuned properly and the center tune is of a bit to the left or right, this can be tuned in. Some units have a center tune zero adjust, others have a Discriminator coil adjustment on the FM board IF section. You will need to look at the service manual in the FM adjustments to see what they call out for certer tune adjustments.

AM adjsutments are similar to FM. I usually just do the screw adjustable cap adjustments for AM. There are a number of other am adjustments but I usually find that just doing the screw cap adjustemts are fine.

Good Luck!!! Feel free to ask any questions if you get stuck
 
Low end adjustments pictures

View attachment 721163 View attachment 721165 View attachment 721166 View attachment 721164

You should go back to the high end adjustments to see if they have gone off peak. At times you need to go back and forth a few times to get the proper peak for low end and high end.

Other differences to mention are that
1) some tuner front ends have both the tuning adjustment caps, and tuning adjustment coils incased in metal with only an access hole. Others have only the screw caps encased in metal, with no top cover for the coils, and some have both the caps and coils exposed.
2) If the unit doesn't have a signal meter, and only has a center tune meter it is a lot trickier. I only mess with them if they are bad. The way I adjust is identify the current position of an adjustment, turn until the station mutes off, that turn back the other way until the station mutes off, and finally put the adjustment screw, or hex coil adjustment at the midpoint between the CW shutoff, and the CCW shutoff.
3) if you have it tuned properly and the center tune is of a bit to the left or right, this can be tuned in. Some units have a center tune zero adjust, others have a Discriminator coil adjustment on the FM board IF section. You will need to look at the service manual in the FM adjustments to see what they call out for certer tune adjustments.

AM adjsutments are similar to FM. I usually just do the screw adjustable cap adjustments for AM. There are a number of other am adjustments but I usually find that just doing the screw cap adjustemts are fine.

Good Luck!!! Feel free to ask any questions if you get stuck

One thing I forgot to mention is to make sure the Tuner, and IF and MPX B+ voltage is right on. If this is low or drifting, the tuning could be drifting all over as well.

I thought about some down and dirty FM IF adjustments, and FM MPX adjustments but they can be really different from each manufacturer, and even for consecutive model numbers for the same manufacturer. But my experience has shown that most alignment issues are with the Front end. The only items I adjust outside of the front end are usually just the discriminator coil for center tune center, and variable tuning pots for FM muting, FM Signal strength (after front end tuning), and stereo threshold level.
 
IMO, these "poor man's" alignment techniques can work far better than you might think. A hint- when using broadcast signals, they're often stations you might not otherwise listen to, and won't instantly identify them. If you have a second radio tuned to the station, playing quietly in the background, it will be instantly obvious if you're aligning to the right station, no matter what the next song is.
 
Thanks Tom!!! Above and beyond the call of duty. I am going to start with my 780. Only three gangs and looks like the easiest to start with. I will keep you up to date. I deoxed the switches and balance and volume controls. The dial string was not on right so I have to reset the dial pointer to the scale and go from there.
 
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Jim,
I had been asked for this by another AK'r last week, and when I saw your post, I figured it was time to do it.

Good luck with the alignment.
Tom
 
Read the factory manual on the SX-780 regarding alignment, particularly about linearity.
 
I read the factory manual and to adjust vc1, 2,and 3 you have to bend the vc blades with a spatula. Not going to do that. I left tc1,2 and 3 alone. The receiver is pulling in stations fine all up and down the dial. There is a harshness to the sound though. So I figured I would try to adjust the outer core of t2 for distortion. It looks as if the adjuster is broken out unless it is way deep in the can. I have included a picture for you to see. Only paid a dollar for this receiver.
 

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IMO, these "poor man's" alignment techniques can work far better than you might think. A hint- when using broadcast signals, they're often stations you might not otherwise listen to, and won't instantly identify them. If you have a second radio tuned to the station, playing quietly in the background, it will be instantly obvious if you're aligning to the right station, no matter what the next song is.

Poor man is right especially with BOTL and MOTL receivers that are not worth paying for bench time. My success rate is 3 out of 4 for curing no stereo and weak reception condition. The poor man's fix is sometimes the difference in being able to sell or not.
 
I expect this to be very helpful when I get the non metal tools -- had them years ago when I had no idea of how to align things and no way of finding out, so never used them and they've disappeared. Thanks to all, especially Tom.
 
I understand about bending the VC plates. If the tuner is tracking with linearity there should be no need to adjust this. I've done a few, and it is very intensive.

As for the lower core of T2, there is a hole in the bottom of the board to access the core for adjustment.

However, if the distortion is due to crosstalk you may want to note the initial position of T1 then adjust that slightly (counting turns) to attempt to clean the signal. If no improvement is made, return the core to its initial position.

It may be more important to get a better setup of the VCO to get as close to 76kHz on the decoder. A reasonable adjustment method is to find where in VR1's rotation the stereo lamp transitions from OFF to ON (NOT from ON to OFF!) in both the CCW and CW directions, and then adjust to the midpoint of those two thresholds (split the difference). Alternately, if you have a frequency counter, with NO stereo signal (inter-station static) just adjust TP23 to yield 76kHz.

VR2 is a pilot subcarrier null adjustment, and you need a quiet stereo reception or a high pass filter to see the 19kHz and above signals and adjust VR2 for their lowest amplitude (on a scope). With an FM generator we can send a "quiet" test tone so only the junk shows up. This is very difficult if not impossible to adjust without instruments, but if you note the initial position and are willing to attempt the adjustment, it MAY quiet down background noise and clean up the signal. It would not be my first suspect, however.
 
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