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tuner dial needle indicator off by 1/4" from tuned station


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#1 dan

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Posted 07 April 2019 - 09:54 AM

any idea how to get the dial needle to align with the actual station tuned in? mine is off by 1/4".



#2 Reli

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Posted 07 April 2019 - 12:19 PM

You will need to take the box apart and adjust the string, or simply change the needle's position on the string.



#3 Fatdog

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Posted 07 April 2019 - 02:03 PM

I would try to change the position of the needle on the string.  Sometimes the needle can be glued in place or clamped on the string though.



#4 Transistorized

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Posted 07 April 2019 - 05:11 PM

Hi Dan. Mine is too. I spoke with Superduper on this. I mentioned trying to slip the string but he informed me that it would end up relocating back due to the flywheel spring setup....and as Fatdog mentioned, the plastic doodad that moves the pointer is glued into position on the tuner string with epoxy. I thought about trying to relocate the glued plastic piece but chickened out :lol: I believe Superduper had mentioned that the culprit was likely due to the tuner drifting over time, coils being bent or turned from a previous entry inside the box at another point in time or not being precise from the factory.

 

The instructions to calibrate this tuner are either difficult to find or unobtainable...and to do it correctly, the tuner would need to be calibrated with frequency generator test tones and special equipment.

 

When it was all said and done (since the radio picked up stations fine) I opted to leave well enough alone... :lol: The only thing you might get lucky with is if the floating pointer flanges to nylon block were not lined up correctly (if ever disassembled for repair).

 

An interesting fact on these. When they put these together at the factory, they lined up the pointer to tuner string (plastic doodad) using a slot behind the dial glass. After the pointer was slotted to the tuner string they then glued the dial glass into place (which covers up the access hole). Unless you knew what it was for and/or had the dial glass off the box, you wouldn't know that it was there or what it was for. Without removing the dial glass you can line things back up with the top cover removed. 



#5 Reli

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Posted 07 April 2019 - 05:23 PM

In my experience most needles aren't even glued down on the string. You can just grab them and move them.  Even if they're glued, just use a heat gun to loosen them up.



#6 Superduper

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Posted 07 April 2019 - 06:01 PM

No, don't listen to any of that.  Needle position on a dial cord was never designed to be moved around.  EVERY dial cord has exacting specifications such as length etc. but the M70 dial cord isn't even physically attached to the needle.  Instead a nylon block is attached to the cord.  The needle just floats freely on the front panel screen.  When assembling the chassis to the front cabinet, the backside of needle is a bent piece of tin with a couple of flanges that matches the nylon block, and assembled correctly, allows the block to nest within those flanges.  Therefore, the moving block pushes or pulls the needle along the dial.

 

You may think that an incorrect needle position must mean that it is installed in the incorrect position.  This is not so.  The reason the needle is off is because the FM band tracking circuitry if out of adjustment.  Therefore this is an ELECTRICAL adjustment and not a MECHANICAL adjustment.

 

To illustrate via a car analogy:

Your car front end alignment is off.  On every car front suspension, there are numerous tie rods, ball joints, idler arm, pitman arm, drag link, etc. Changes to tolerances, geometry, etc due to wear, accident, improper adjustment, etc. will throw off your alignment.  This can cause tire camber angle (vertical), toe (distance between tire centerline on front vs rear), and caster (steering angle), etc.  But it can also cause your steering wheel to become off center.  To remove a needle and reaffix it to where you think it should be would be akin to removing a steering wheel, and putting it back in a different spot.  Yes, shadetree mechanics have been doing that forever.  No, it's not the right way to fix it.  The correct way would be to align the front end.  

 

The correct way to fix a tuner needle position is to align the tuner's circuitry.  Note that band tracking circuitry also often affects the band coverage too.  In other words, you might notice that the needle is off at 92.1 because that's where your favorite station is located.  It's also possible that the needle at 106.5 is spot on or even far worse off.  Moving the needle therefore only makes it accurate at the spot you moved it.  Yet, the tracking is still off.

 

Now the bad news:  I don't see a service procedure included in the SM for the M70 for tuner tracking.  It is included in tuner adjustment instructions for virtually every tuner, or sets that include a tuner.  Luckily M70 tuners have proven to be fairly reliable, unlike Sanyos that seems to always need fixing.  Can it still be adjusted?  Most certainly, but you'll need a specialist who knows what coil to tweak.  Indiscriminately playing with the coils will most likely lead to irreversible damage to the alignment.  In the end, I suggest you just leave it alone.  1/4" off isn't that much, and it's not like you don't know what station you are listening to.  Most folks know exactly what station is playing the moment it is captured while turning the dial.

 

Lastly, Transistorized is incorrect in that the tuner needle would be lined up at the factory and glued.  In fact, every tuner cord and needle locator is certainly built on a jig based on specifications.  Therefore, they are all identical and a used cord from a different boombox installed in any other boombox of the same model should still locate the needle in the exact same spot.  Additionally, the tuner boards are probably electronically aligned on another jig which duplicates the needle positions based on the varicap wagon wheel position.  I'm sure that if any discrepencies manifest after everything is assembled together, further alignment "in the box" is conducted until within tolerance.

 

Mechanically speaking, the tuner needle should rest at 88 MHz on the low end, and 108 MHz on the high end, and travels between these extremes.  If you moved it 3 MHz to the right, it will now be parked at 88.3 MHz on the low end and travel past the scale to 108.3 MHz on the high end.  If you understand this, then you'll also understand why any changes need to be performed electrically and not mechanically.  It's not the needle that needs moving.  It's the tuner is not electrically tuned to the proper frequency to match the needle position.



#7 Transistorized

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Posted 07 April 2019 - 06:53 PM

You're right. I phrased that wrong as it sounded as though I was talking about tuner to cord frequency alignment.

 

My reference to the hole behind the tuner window was more for when assembling the chassis to the front cabinet. Sometimes it is difficult to see (during assembly) when the nylon block is mated and centered with the metal flanges of the floating metal pointer. That hole, prior to gluing the front tuner window onto the face of the box, makes this alignment of the block to the pointer flanges a cinch :-) However, this in no way has anything to do with the alignment of the tuner frequency to pointer position as this would have already been set prior to assembly.

 

 



#8 dan

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Posted 18 April 2019 - 12:48 AM

All the am and fm stations and as far as I can tell the shortwave, as well, were off by 1/4 inch no matter where on the dial. I broke of the red adhesive carefully from the string and the nylon block and moved it over. I glued it in place with hot melt glue.

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