1225. Arm moves towards spindle when balanced

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nonost
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1225. Arm moves towards spindle when balanced

Post by nonost » 13 Jan 2020 22:58

Hi! I've been dealing with a 1225 and I have one last problem. Everything else is done. The problem is the arm moving towards the spindle when tracking force and anti skating are set to zero. The arm is well balanced and I also cleaned the horizontal arm bearing.

I've removed the cue lever, the shut off lever and desoldered and checked the wires. The problem is the AS system. I know it because when I remove the skating lever completely(241) the arm stays in place. The force is stronger near the post. In order the stop this force the arm needs between 0.25 - 0.5g of anti skating. With that anti skating force the arms stays in place almost in every point along the path through the spindle. BUT near the end of the path this anti skating force is too much and it moves the arm backwards a little bit.
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Well, the plastic part 238 is a little bit broken. Here a pic:
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You can see the gap just before the "1209" print, at around 10:00. Could be this the cause? Would a new one solve the problem? In this picture the anti skating lever is at zero position. I've always wondered if in this models the little circle in the black plastic should be "in line" with the screw to its right. In this unit the little circle is not in line with the screw, but it is close.(I'm talking with the lever at zero)

I hope I can solve this since everything else is working great so far.

Thanks!

lenjack
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Re: 1225. Arm moves towards spindle when balanced

Post by lenjack » 13 Jan 2020 23:46

Did you check that it's level?

DSJR
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Re: 1225. Arm moves towards spindle when balanced

Post by DSJR » 14 Jan 2020 00:46

The issue is the broken cam as I think you've worked out. Study of many Dual service manuals indicates that proper 'zero' when the arm doesn't move at all is when the end of the anti-skate spring is directly in line with the horizontal axis of the tonearm bearings as shown in numerous pictures in practically all the relevant service manuals (fig 9 in the 1224/25 manual). The crack and subsequent 'opening' of the disc has ruined the original calibration and, before trying to 'adjust' this, I'd try the likes of 'organdonorparts' to see if they have a replacement. With correct part number, Dualcan may be able to search through his inventory perhaps?

Also, can you check the parts lists to see if this part is shared with other decks using 10" platters? It may possibly be.

Unless I'm mistaken, practically all Duals of this period had dynamically balanced tonearms to a very high degree, even in the lower models in the range. Although this model lacked the 'gimbal' style bearings, I'm pretty darned sure that these 'lesser' models were still pretty stable if the deck was tilted.

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Re: 1225. Arm moves towards spindle when balanced

Post by dualcan » 14 Jan 2020 00:57

Hi,
You need to correct the mechanical zero adjustment.
If you look at the green oval:
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the 7 mm (?) bolt that sits sideways is the zero (arm movement) adjustment. Turning it clockwise will bring the (balanced, no anti skating, no tracking force applied) arm swinging towards the record center whereas counter or anti clockwise will bring it to the arm rest. I may have it backwards but either way, the adjustment is found somewhere in the middle and you will find "inner peace" for the arm. Most likely anti skate lever 241 got a tiny bit out of shape. Once the arm is no longer a traveling gypsy, reseal that bolt with some nail polish.
Before everything else however seal nut 239 (in the red circle) as when that oval is upset, the AS force will be adversely affected.
Regards,
k

nonost
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Re: 1225. Arm moves towards spindle when balanced

Post by nonost » 14 Jan 2020 23:45

Hi! Thank you guys :)

The little screw did the thing. The arm floats in place throughout half the arc. Through the other half (close to the spindle) the arm moves towards the rest post. This happens with and without the AS. So I would say the AS problem is solved. The problem now is the arm moving towards the rest post, but only in the second half of the arc.

I've disassembled the arm in order to check the vertical bearings. One of them was dirty. I've cleaned them and checked that the arm was straight. The problem still happens.

Since I couldn't think anything that may be disturbing the lateral movement even without the AS system in place, I removed the plate under the tone arm where you find the pimpel and one of the horizontal bearings.. I did clean them days ago but something strange happened this time, this little thing felt off when removing the two nuts:
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I've never seen this before. Any idea?

Also, I've noticed that the bottom left metal retainer is missing. It doesn't seem important to me...
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dualcan
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Re: 1225. Arm moves towards spindle when balanced

Post by dualcan » 15 Jan 2020 01:56

Hi,
The indicator goes here:
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As far as the arm moving, you have found the middle point for the AS lever. This is when the arm stays motionless in the middle of the playing surface. If the arm still wants to move when nudged either way after that "sweet spot" there needs to be another adjustment made. First the anti skate spring needs to be in perfect shape, especially the hook end that hooks into the AS lever (241). If the spring sits crooked then we have a problem. Next let's have a look at the specific parts:
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In that pic, there are two red dots, the first is the needle tip from the central arm support - it is the epicenter of the arm.
The other dot is the eye of 241, that the AS spring hooks into. The adjusting bolt 243 you used to keep the arm motionless moved the AS spring along "east / west" axis (green line) aligning the two dots. If however that lever 241 got slightly stretched or "shrunk", along the yellow "north / south" axis, then the AS spring will still pull the arm, once your adjusted "sweet spot" is breached. The gist here is that the AS spring hole in 241 (second red dot) and more specifically the actual AS spring curl that attaches to the red dot, needs to be exactly over the arms epicenter. Once the east / west is corrected with adjusting bolt 243, double check if the north / south position of the spring curl is over or underin relation to the arm's epicenter.
Lever 241 has a purposeful narrow end where the angle can be increased or decreased (red line). You won't see any factory bent marks because we used special tools that don't leave any marks. Be careful if you need to bent, because a little goes a long way, and you don't want to jeopardize the "flatness" of 241. The two axis need to be checked against each other and in case the north / south is adjusted the east / west needs at least a look-see...Once the spring sits perfectly, the arm can no longer be pulled by the AS spring, because any pulling on the epicenter of the arm does not give the spring a triangulation effect. It's only when one of the axis is off that a force-triangle forms between the two ends of the AS spring and the arm's epicenter, allowing the spring tension to pull and that the fun begins!
Remember these arms have very low bearing frictions and horizontally, it is about 0.4 mN or 0.04g. The maximum force that the anti skate spring can be dialed in, is about 0.4g (slightly less than 1/10th of max tracking force > 5g. The slightest error on the A S spring position will overcome that tiny arm friction.
Regards,
k

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Re: 1225. Arm moves towards spindle when balanced

Post by DSJR » 15 Jan 2020 21:50

Have we confirmed if the little 'cam' is cracked through or not? I appreciate the error can be adjusted out by the nut as Klaus indicated, but it still looks broken to me...

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Re: 1225. Arm moves towards spindle when balanced

Post by dualcan » 15 Jan 2020 22:30

Hi,
These later manufactured black ovals , although still having the 1209 number (which it will also fit -plus a ton more- are made of a tougher plastic. The usual crack in the earlier ones, occurs across the secondary (aligning tool) hole.This does not look cracked but the area is waay too liberally coated with lube. The glyptol seal is scuffed but I'd venture it is still intact-maybe in need of a bit extra.
Regards,
k

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Re: 1225. Arm moves towards spindle when balanced

Post by nonost » 17 Jan 2020 02:27

Wow...thank you Klaus. I really appreciate it. That's great info and I'm happy to learn how the anti skating works. The triangulation effect is magic.

Is the first red dot in the center of the circle? The needle from the arm support sits just below that so that would make sense. But I have my doubts...In the picture you put the red dot a little bit "miscentered" and after taking a look at my 1225 and 1235 I was wondering if that was on purpose. In my units the spring hook is a little miscenterd as well.

With bolt 243 I can easily center de east/west axis but decreasing the angle in 241 didn't make much difference. I can center the hole where the spring hook goes but the spring hook remains a bit above the center.

Anyway, I screwed up the metal thing that gives tension to 241...I guess I have to look for a replacement.

As for the cam issue, is not really cracked through. The crack stops just a bit after you can see in the picture. Thanks to you too DSJR, you're always helping patiently. I've read lots of messages from you in this forum.

Thank you very much!!

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Re: 1225. Arm moves towards spindle when balanced

Post by dualcan » 17 Jan 2020 20:19

Hi,
The red dot in the center of the yellow and green lines represents (or is supposed to ) the needle point which is visible through the hole on the AS arm:
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It is the perfect azimuth between the needle point and that hole / AS spring hook-up curl, that will give you zero pull on the arm. Any deviation existing between these two (needle point and curl) , will cause a triangle and therefore pull from the AS spring.
If by chance you are referring to the prawn spring (item 240) that forces the AS arm (241) that can be simply rotated the "wrong way round" until the extended arm hits the chassis wall again. Prawn springs release when turned against their curl and tighten grip when turned into the curl.
Remove the AS arm (c clip 242) and swing the spring around. If needed, straighten the spring's arm.
Regards,
k

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