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Dual 1245 Speed Problem

M

mcdmgb

AK Subscriber
Subscriber
Picked up a Dual 1245 yesterday and can't get the pitch control to have any effect on speed. It runs fast at both speeds. The control is connected by a toothed belt to a toothed pulley which it rotates, but for the life of me I can't see how this is suppose to effect the platter speed. Anyone have any ideas?

Mike
 
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That tiny belt does break. Are you certain that it is turning the gear at the motor? I seem to recall that the way it works, is by raising and lowering the top motor spindle support bracket. This forces a spacer down into the pulley. Why? Because the pulley is segmented like an orange, and by forcing the sections further apart, the pulley gets fatter, thereby altering pitch.

Seth
Forever Analog
 
Seth is right about the belt. Lift off the platter & you'll see it beneath the motor pulley. If it's missing, there's another fix. You need a 5.5 MM nut driver On top of the pulley is that 5.5 MM nut, probably with blue lock tite on it. A little turn counter clockwise will slow it down. Trial and error here.

bill@fixmydual.com
 
the belt is intact and moving the toothed pulley. I have moved the hex nut both directions and at has no effect. Should I remove the hex nut and disaasemble to see if something is frozen?

Mike
 
You need to see whether the segmented motor pulley is expanding and contracting or not, by seeing if the spaces between the segments change their gaps, Mike. It won't be much, but it can be seen.
Here's a blowup of the pulley assembly.
Tom
 

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    pulley.jpg
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Nice pic!

#15 is the motor pulley. I wouldn't go adjusting that. The placement on the motor output shaft is a pretty close tolerance. That's so the belt stays on the platter on both speeds.

BUT, on top of the motor pulley (#15) is an insert that moves up and down when you adjust the pitch (not separately numbered). This insert makes contact with the top mounting boss, and when you speed up the pitch, the pulley moves up, the insert has contact with the boss, forcing it down into the pulley, expanding the pulley, increasing the speed. Likewise, when you slow it down, the pulley goes down, a spring underneath the insert pushes it up, making the diameter of the pulley smaller and slowing it down. Put it on full slow pitch. See if the insert (chrome in color) is making contact with the mounting boss. if not, it's frozen in the pulley. A LIGHT TAP (I know how much Seth likes hammers) on the chrome insert with a small block of wood should free it up. No oil or WD-40 - it'll get on the belt!!

bill@fixmydual.com
 
I've hammered on it on the motor pulley and played with the nut on the toothed pulley. I see some movement of the motor pulley, but it still doesn't seem to do anything. If I run the nut on the toothed pulley all the way down it will slow it down on 33.3, but it never becomes steady and there doesn't seem to be any fine control with using this method. None of this had any discernable effect on 45. Its still runs fast. Is there something on the underside that I should check? If so how do you get it free of the base? It seems that the suspension springs won't let it go.

Mike
 
This is an easy problem to solve, for the mechanically inclined.

The vario-pulley is expanded (to go faster) or contracted (to go slower) by a conical plug that moves up and down inside the pulley. The plug's height (and thus the speed) is controlled by a thrust plate that contacts the plug. Changing the speed control moves the thrust plate up and down.

The standard failure is just that the plug assembly gets sticky on the motor rotor shaft it rides up and down on. Exercising extreme care, take the whole mechanism apart. Using q-tips and solvent, remove any hardened grease from the shaft and inside of the plug.

It is often useful to take #1000 or finer sandpaper and resurface the shaft, and to take a "curl" of sandpaper to the inside of the plug.

Once these steps are done and any metal glaze cleaned off, the plug should move up and down freely on its shaft. Thus, the thrust plate can once again take control of the plug and allow the vario-pulley to expand and contract as needed.

Note that even if the speed adjustment belt is broken, there is a hexnut -- accessible through a hole in the platter -- that you can use to adjust the "baseline" vario-pulley expansion to 33-1/3 exactly.

I've done the above procedure hundreds of times over the last 25+ years. It works evey time.

Best,

Fred Longworth
 
Before you landfill it, pull the motor. It has the SM-860. That motor replaced the SM-840 found on 601's and 1249's. The 840 at 60 Hz will intermittantly spin the platter at double speed. No fix but to change the motor.

Throw it on the 'bay as a 601 & 1249 fixer. I have yet to see a 840 motor that doesn't act up.
 
Fred Longworth said:
This is an easy problem to solve, for the mechanically inclined.

The vario-pulley is expanded (to go faster) or contracted (to go slower) by a conical plug that moves up and down inside the pulley. The plug's height (and thus the speed) is controlled by a thrust plate that contacts the plug. Changing the speed control moves the thrust plate up and down.

The standard failure is just that the plug assembly gets sticky on the motor rotor shaft it rides up and down on. Exercising extreme care, take the whole mechanism apart. Using q-tips and solvent, remove any hardened grease from the shaft and inside of the plug.

It is often useful to take #1000 or finer sandpaper and resurface the shaft, and to take a "curl" of sandpaper to the inside of the plug.

Once these steps are done and any metal glaze cleaned off, the plug should move up and down freely on its shaft. Thus, the thrust plate can once again take control of the plug and allow the vario-pulley to expand and contract as needed.

Note that even if the speed adjustment belt is broken, there is a hexnut -- accessible through a hole in the platter -- that you can use to adjust the "baseline" vario-pulley expansion to 33-1/3 exactly.

I've done the above procedure hundreds of times over the last 25+ years. It works evey time.

Best,

Fred Longworth
Click to expand...

Tried the cleaning routine. There was a build-up on the shaft, which I polished off, but it doesn't seem to make any difference. If I really crank down on the hex nut I can get 33.3 close, but 45 is a lost cause. Any other thoughts as to what to try before it gets recycled?

Mike
 
Not much has recently as some of the best venues have been closed/rezoned/torn down. It's really quite a sad fate for the home of greats such as Eddie King, Luther Alison and Richard Pryor.
 
Thank you Fred. You confirmed what I suspected but was just too chicken to try. Disassembled and cleaned a 1245 and 1249 and now speed control works perfectly. On both tables the mechanism that pushes down on the segmented pulley was too high plus the they were both sticky - one would not even close the segments. Also, this may be a well-duh, but note that the motor has to be pulled, this little helpful tidbit is not mentioned in the Dual service manual.
 
Hello All,

Jumping in on this thread (despite it being legally able to drink in my Region) . I have a few Dual Turntables that have the SM-840 motors in them (2 x 1249 + 1 x 601) and a 510 with a SM-860 in it.
One of the 1249s is having the double speed issue.
The other 1249 and the 601 have has had limited use by me. But have yet to reveal this issue.
The damn 510 works and sounds great... so I would like to leave it with the sm-860.

I have read about the module, and the SM-860 Motor/Winding swap.

I am beginning to wonder, is it an actual motor issue, or is a belt issue? Have many had the issue then changed the belt to have the issue resolved?

Not completely sure it is worth me asking, as I will just try and find out for myself. But I am wondering if the Module (if I can even find it) is worth doing as I have watch one be removed for chattering the motor.

Anyway... if there are some out there that have had this issue and then it went away with a belt replacement, I would like to hear from you. Or alternatively those that changed the belt (with a good one) and the issue remained.

Wishing Happy Spins to all!

Cheers,
Fitch
 
Fitch1 said:
Hello All,

Jumping in on this thread (despite it being legally able to drink in my Region) . I have a few Dual Turntables that have the SM-840 motors in them (2 x 1249 + 1 x 601) and a 510 with a SM-860 in it.
One of the 1249s is having the double speed issue.
The other 1249 and the 601 have has had limited use by me. But have yet to reveal this issue.
The damn 510 works and sounds great... so I would like to leave it with the sm-860.

I have read about the module, and the SM-860 Motor/Winding swap.

I am beginning to wonder, is it an actual motor issue, or is a belt issue? Have many had the issue then changed the belt to have the issue resolved?

Not completely sure it is worth me asking, as I will just try and find out for myself. But I am wondering if the Module (if I can even find it) is worth doing as I have watch one be removed for chattering the motor.

Anyway... if there are some out there that have had this issue and then it went away with a belt replacement, I would like to hear from you. Or alternatively those that changed the belt (with a good one) and the issue remained.

Wishing Happy Spins to all!

Cheers,
Fitch
Click to expand...
The sm840 motor doesn’t lock to 60Hz at startup, but if you add a little resistance (slow the plater with your finger) at startup, the motor will lock in to 60Hz.
This is the same thing a new tight belt can also do, but eventually the belt stretches. The module somehow uses this same phenomenon to lock the motor to 60Hz

I’ve had the module in my 510 for about 10 years and it’s never run a double speed.
 
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