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Old 9th April 2008, 12:55 AM   #11
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If this many bright people can't figure it out, it's going to turn out to be something really dumb.
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Old 9th April 2008, 09:54 AM   #12
Miti is offline Miti  Scotland
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Fran

Sorry... No - it's a 2-pole, only has 2 wires to it... But I will take a close-up look at the wiring on the motor, just in case M-S have hidden such an arrangement on/near the motor mount...

Ta!

Miti
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Old 9th April 2008, 10:31 AM   #13
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Try a thicker belt to get a relative increase in the diameter of the motor pulley and a faster speed.

sp
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Old 9th April 2008, 11:43 AM   #14
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by makinson1

If this many bright people can't figure it out, it's going to turn out to be something really dumb.

Quote:

So, since then, I've tried to check the platter speed with
a strobe disc (50Hz to suit UK freq) - the strobe bands rotate
anti-clockwise on both 33+1/3 and 45 rpm. Neither sits stationary...
Hi,

The chances of a strobe disk being stationary are near nil ......

A "solution" is to use spray paint on your turning motor spindle .....

Typical turntables of the MB10 ilk use a 4 pole shaded pole motor.
It is synchronous and only has two wires, i.e. the 240VAC power.

/sreten.
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Old 9th April 2008, 01:54 PM   #15
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Did you do the count with the tape on the platter yet?


It'd give you a good idea of what degree of being slow we're talking about here.

Fran
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Old 10th April 2008, 08:47 PM   #16
Miti is offline Miti  Scotland
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Hi Fran

Yes. I completed the speed tests, cleaning and motor checks...

I did the speed test 6 times...

1st pair: TT revolving @ 33+1/3, "free-wheeling", no vinyl:

Both tests = 95.5 revolutions in 3 mins (digital timer).

2nd Pair: TT revolving @ 33+1/3, vinyl on TT, stylus applied:

Both tests = 95.5 revolutions in 3 mins (digital timer).

3rd Pair - Belt, platter & motor spindle cleaned with White Spirits. All dried (kitchen towel) and refitted. TT revolving @ 33+1/3, "free-wheeling", no vinyl:

Both tests = 96 revolutions in 3 mins (digital timer).

So, a slight improvement after cleaning with spirits, but still 4% slow...

I also checked the motor for "cogging" - There's no sign of this, the motor spins freely and smoothly... BUT, there is a LOT of end play in the motor spindle.. Is this normal..? It moves up/down about 4 mm - I only discovered this when spinning the motor twixt thumb & finger, it doesn't seem to move when in operation...

And, Sreten, your're right... It's a 4-pole, shaded pole motor... Just 2 wires going to it, 1 live, 1 neutral...

So... Do I "accidentally" drop the refrigerator onto it and phone my insurance company, or is there still hope for the old girl..??

Miti
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Old 11th April 2008, 02:20 AM   #17
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What baffles me is that you say the motor has lots of torque and doesn't seem to be cogging.

Wait a second. Who cares if it's slow? Just dump the analog output into your computer and fix the slow temp in the software!

Sell one of us the Micro Seiki and get yourself one of the Scotish turntables :-)
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Old 11th April 2008, 02:53 PM   #18
Miti is offline Miti  Scotland
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Quote:
Wait a second. Who cares if it's slow? Just dump the analog output into your computer and fix the slow temp in the software!
Now I wish I was at home with the software manual and not here at work... I hadn't even considered that..

Might be a viable option... For the A-D transcription anyway...

I would still like my turntable working though... Even with the 4% slownessosity I still prefer the sound... I've always felt that CD's sound like you're listening to them with a slight case of tinitus... Know what I mean...? (Is that AAA snobbery..?)

I'm wondering if the speed problem could be supply voltage related..?? My limited understanding of AC motors tells me that the speed of rotation is supply frequency related though...

I think the application of paint or lacquer to the spindle may be worth exploring and I may take the motor out for a close-up inspection, pending identity of available spares... (Ha!, who am I kidding..??)

Miti
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Old 11th April 2008, 05:25 PM   #19
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Can't understand what would be wrong here. Yes, the speed is frequency dependent, and that will be better than the 4% you see.

Have another look at the motor pulley. Is it a flat pulley with a "domed" centre? If thats the case then you will need to adjust the motor mounting to get the belt to ride on the high bit of the pulley rather than down in the gully on either side. Usually there is one bolt that can be screwed in or out a bit to adjust the angle that the motor is at relative to the platter.

If its running the low bit all the time then that would be a source of your problem.

Fran
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Old 11th April 2008, 07:04 PM   #20
Miti is offline Miti  Scotland
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Fran

Quote:
Have another look at the motor pulley. Is it a flat pulley with a "domed" centre?
Hmm.. Not 100% sure what you mean here... The motor has stepped "spindle" rather than a "pulley"... It has 4 well-defined diameters:

The bottom of the spindle is the widest part - it has a hollow centre that is a very close fit on the motor shaft and a single gub-screw that secures it to the motor shaft. It's NOT loose...

The next section (45 rpm drive) is slightly narrower. It steps down in dia by about 4 mm from the lower section (90 deg edge on the step). This section is a "parallel cylinder", no "high or low spots"

The next section (33+1/3 rpm drive) is slightly narrower again. It steps down in dia by about 4 mm from the lower section (45 deg edge on the step to facilitate a smooth belt transition between the two drive areas). This section narrows slightly at the top & bottom, giving the spindle a slightly rounded appearance here... But the overall length of this section isn't enough to allow the belt to ride away from the widest point..."

The topmost section of the spindle steps up in dia again - looks to be the same as the 45 rpm section... This also has a 90 deg step edge and forms a kind of "cap" to prevent the belt leaping off the top of the spindle...

So... There aren't any low areas where the belt could be lazily biding it's time... the two drive sections are parallel... The belt seems to be transitioning from one to the other quite nicely, there doesn't feel like there is any "slip" in the drive-train...

What is the significance of "cogging"...? I can't feel any problems with the motor armature - it spins quite freely and my test of the motor's torque is a very subjective one, 'cos I've notheing whatever to compare it to... Would a "good" motor spin me around the room a la Tom & Jerry? or is it about right that a firm pinch will stop it cold..??

I've tried playing with the motor spindle when it's running - lifting the shaft up seems to induce a "cogging" effect and it's quite easy to stall the motor, but when it's in it's normal position, it runs very smoothly with considerable torque...

I'm considering the application of some thin heat-shrink sleeving to the 33+1/3 section (I play my 45's on a 1964 Wurlitzer Jukebox, so that's not a problem at the moment...)

Miti
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