TT Synch Motor - Extreme Vibration

[seabass23]

My Dad's Pioneer PL-A45D, full-auto belt-drive TT that has developed extreme motor vibration. The tonearm will literally dance across the record. At first it was an intermittent issue that has now become permanent.

At first, I assume it was a mechanical failure of the motor but he says the motor spindle and platter spin smooth by hand.

Could this be an electrical issue? Not much to the circuit (schematic is attached). PM is the drive motor and WM is the cueing motor.

If I had it in my hands I wouldn't bother you guys with this question, but it's at his place. Would failure of one of the caps cause this or should I write this off as mechanical failure and find him a new table?

[Number13]

I have had that occur when the belt becomes deformed
from sitting too long, Have you tried a new belt?
You should also check the motor spindle for any
bits of old belt.

[seabass23]

Originally Posted by Number13

I have had that occur when the belt becomes deformed
from sitting too long, Have you tried a new belt?
You should also check the motor spindle for any
bits of old belt.

Thanks for the suggestion but I believe it is a motor issue. I should have mentioned that belt is new and he confirms that belt belt drive is clear of debris and belt is properly aligned and installed.

[Number13]

Hmmmm.
Not really much to those old motors, they either work
or they don't. I would suspect the platter bearing next.

[kevinkr]

Some more diagnostics need to be done before coming to any conclusions.

I'd have him run the turntable with the arm cued in a non playing position and feel the plinth for vibration. Is it high frequency vibration or very low frequency indicating that the motor bearings or internal component have failed or the main bearing has failed.

Next I would have him take the belt off of the motor and see if the vibration levels change at all.

Have him check that the platter spins smoothly for some period of time without the belt installed. There should be no discernible vibration at all if the main bearing is OK, and the spindle is not bent. Thrust plate and main bearing bushings OK?

When was the last time this turntable was treated to a good cleaning and lubrication?

Is it possible that the automatic cuing system is not fully disengaging and causing this problem? (Congealed lube or broken component?)

Is the cartridge installed correctly and tracking force and anti-skating at recommended values? Stylus fully seated in cartridge body? Worn out cartridge? Has he checked?

Some inexpensive synchronous motors had multiple piece rotors and the adhesives give up due to age resulting in a severely unbalanced motor. (I recently encountered a Garrard changer that had this problem and had to repair the motor..)

[Number13]

Of course you are right, kevinkr.
You can't really diagnose anything by phone or internet.
Just a guess on my part, but since this a Pioneer my thought is that
it has the same problem most older PL models seem to have, a disintegrated
bearing disc at the bottom of the spindle bearing tube.

[kevinkr]

Originally Posted by Number13

<snip>
Just a guess on my part, but since this a Pioneer my thought is that
it has the same problem most older PL models seem to have, a disintegrated
bearing disc at the bottom of the spindle bearing tube.

Could very well be.. Something to think about. I always find it amazing that so many people expect a turntable to run forever without any significant maintenance. Cheaper tables regardless of maintenance also often have irreplaceable components that just wear out..

[3GGG]

Could be one phase of the motor not working, causing extreme pulsating. Maybe replace the small cap on the motor, or replace the motor.

[Number13]

Oh man, you should see the junk people haul in here
expecting me to make run.
Christmas time especially. I am fielding roughly
one call an hour about making grandma's old console
play again. After 30 years in the garage.

[kevinkr]

Originally Posted by Number13

Oh man, you should see the junk people haul in here expecting me to make run.
Christmas time especially. I am fielding roughly
one call an hour about making grandma's old console
play again. After 30 years in the garage.

Can totally relate from past experience.

Good luck! And ultimately a Merry Christmas..