[rcag_ils]

Question,

The speed of my Heybrook TT-2 shows a bit slow on the strobe disc (dot drifts CCW). I took it apart, there's a .15uf/250V cap in parallel with two wires. There are two .015uf caps with the AC and the on/off switch, but I think these are for trancient noise reduction.

Assuming the motor is good, which I think it is, because it's very quiet and smooth. The previous owner solved this problem by increasing the pulley diameter,(by putting a piece of plastic tape around the pulley, I don't like it). Could change the cap value, or have you heard the cap drifts out of tolerence and cause problem like this? Is there a universal cap value for turntable AC motor?

[Wayner]

The two .015 uf caps are to stop switch make/break noise. The .15uf is a stater capacitor and has nothing to do with motor speed other then to start the motor. I would only replace with same values.

You are correct that a CCW direction indicates that the motor is slow, CW is too fast.

Solution: Ignore it. If it's drift is slow, I just woudn't worry about it. The fix is either a larger pulley or smaller drive rim diameter.

Wayner. 

[Wayner]

I've had another thought on this topic that Berndt brought up a while ago and that is oil viscosity. That's right, too thick of a lube in the platter bearing may slow the whole damn thing down, too light may not take up enough gap and cause bearing noise.

So, now if we have a pretty stiff lube in the bearing, slowing down the motor, perhaps it's time for a cleaning. I'd clean the whole bearing out and try a lighter oil. That may help things along to make the drift much more acceptable, or perhaps with luck, eliminate it altogether.

Wayner

[Elizabeth]

Belt. The belt 'centerline' is the belts' effective diameter. Thicker belt: faster turning table. Thinner belt, slower turning turntable.
I read this somewhere.

[rcag_ils]

Wayner, doesn't the .15uf cap have something to do with the timing of the motor?

As far as lubricant goes, I cleaned the bearing well, and spindle bearing, there wasn't that much to clean, it was very clean to begin with, even I have not fill it with oil yet, but it still have a coat of oil on it, so I doubt that the oil's causing the slowness of the motor.

As far as the belt, if it has anything to do with the belt, it would be because it's too tight. The thickness of the belt looks to be correct by judging how it sits on the pulley.

[Wayner]

Belt. The belt 'centerline' is the belts' effective diameter. Thicker belt: faster turning table. Thinner belt, slower turning turntable.
I read this somewhere.

I think if it's a flat belt, that might not be the case, tho there probably is some stretch and compression going on. I wouldn't put it at the center. Round belts offer a different senario, and it might be some point on the v-pulley contact, but then transfers to surface contact on the platter rim. That one is  a tuff one to picture.

Wayner

[royphil345]

Yeah... The motor pulleys are usually a little larger in the middle, so a wider belt can increase speed a little. A loose belt can slip a bit and it's hard to detect. Also, they can wear or stretch to a narrower width. A new belt may be the answer if it's a couple years old or more.

There may be something to those capacitors though... Maybe you're getting some sort of loss due to a bad one. I had a cheap MCS Series table I picked up that ran slow no matter what and I couldn't figure it out. Nothing seemed wrong mechanically... It had a capacitor across the motor terminals and maybe another for the switch. I suspected they were probably the cause. It was a cheapo table and I threw it out rather than messing with it though. Couldn't hurt to pick up a few new caps and give it a shot.

[Wayner]

You can run the motor without a capacitor, but you'd have to start it by hand to get it going. That is how you can tell the cap is bad, because the motor has poor starting, but lots of torque when up to speed. One of my Hurst motors started to start poorly (with out help) and I soon discovered one of the cap leads was actually broken off. The table ran fine otherwise. I should mention that this is the case if the motor is a synchronous type. That motor locks onto line frequency (60 cycle) to keep it's speed.

Wayner 

[rcag_ils]

So does it mean that in my case, the motor being a little slow is just the way this motor's made?

I also remember in some motor, there's a resistor in series with the cap, and depending on US voltage, or European voltage, the resistor need to be in different value accordingly.

[Wayner]

I don't think you can remedy the situation.

Wayner

[royphil345]

The cap being missing from the circuit would be completely different than a bad cap being in the circuit. I think it would be worth a shot to replace them. Also... new or wider belt.

[rcag_ils]

I think the cap and sometimes with a resistor determine the phase of the motor, they are different for 250rpm and 300 rpm, 50hz and 60hz in line voltage, not a start up cap.

[Wayner]

Motor direction is determined by how the motor is wired. Most synchronous motors have 4 wires.

 

The number of poles and the line frequency determine it's speed. They run on line frequency (cycles per second) not voltage variation (to a point), so resistors have no use and the cap is used to start the motor.

Wayner

[rcag_ils]

http://www.mclennan.co.uk/datasheets/european/synchronousdata/990411131813.pdf

Depending on the motors, some of them require resistor, and different value of cap to run correctly, above is just one of many examples. Doesn't appear to be a start up cap, or motor run cap like those in the air conditioner. Maybe if I used a .18uf instead of a .15uf, the speed would be correct.

[Wayner]

The illustration on the pdf shows a 220 volt motor. The resistor is for current limiting and the cap value change is because it is for 50 cycle.

One more time. The cap is for starting the motor. The pole design of the motor locks on line frequency. If we have a 300 RPM motor, that means it goes around 5 times every second. Every single time the motor goes around (one revolution), is does so .2 seconds. Therefore, this motor is a 12 pole. 12 positions (or cycles) every .2 seconds, 60 pole positions every second (5 RPM) and 3600 pole positions every minute for 300 rpm.

Lowering the voltage will change the torque value. Changing the cap will change the frequency and screw up the motor. If you want to change the cap, get one of the same value with a closer tolerance to the theoretical design.

Wayner

[rcag_ils]

It is the same motor for 250rpm and 300rpm, changing the cap to change the speed. Some motors use resistor for 110V, this particular one using the resisitor for 220V.

[Wayner]

That example is a specially designed synchronous motor (I see it's a 24 pole) and not a typical motor used on most tables. It has been specially designed to run on 50 or 60 cycle and 110/117, or 220 volt.

Is this the motor in your turntable or is this one you just happened to find on the internet? This not how these motors normally are made. I hate using Wikipedia, but maybe you should read this.

http://en.wikipedia.org/wiki/Synchronous_motor

A 12 pole motor has poles spaced at 30 degrees apart, a 24 has poles spaced at 15 degrees apart. The 24 pole motors are usually higher torque and physically larger.

Wayner