Right; one problem solved - I think - another's arisen.
I hooked up my 1982-vintage Dual CS-505 and it played stereo through both channels. Not the amp, then. On examining the CD player leads, the central male pin on one channel has no metal, just plastic. Replacement ordered.
Now, is the varying speed on the Dual a belt problem, or the motor objecting to not being used since the summer of 2000? Only a new belt will answer that one...
If the speed is varying, it's almost certainly the belt has perished and lost it's sproing after sitting for so long.
If you remove the belt, it will probably not spring back like a happy rubber band; it will sit there in the shape is has taken up, like saggy old knicker elastic.
Basically, after it's lost it's elasticity, there's not enough belt tension to transmit the drive.
The motor itself is synchronous, so it can't really go at the wrong speed.
The only electronic parts IIRC were a capacitor and resistor to provide a phase-shifted supply for a second winding.
If the motor starts and runs, these are fine.
Bearings can get a bit rumbly, but not to the point it's varying the speed.
It will manifest as rumble in the audio.
So yes, replace the Main Drive belt, I'd say.
(And whilst you are at it, replace the Pitch Control belt too; they are quite brittle and it may well have disintegrated too. Not that it is critical to the turntable's operation, it just means the pitch control knob doesn't do anything any more.)
A couple of tutorial videos..
https://www.youtube.com/watch?v=qMyGKXlJL4Ehttps://www.youtube.com/watch?v=tlEHLvlQ3UwIncidentally, if anyone's curious as to how you do pitch control on a synchronous motor (It does not have Variable Frequency Drive! )...
It's mechanical; a Continuously Variable Transmission.
If you look at either of the videos I linked to above, look at where the main drive belt goes round the motor pulley.
Notice a couple of things about the motor pulley:
- It is stepped, this is the 33-1/3 vs 45 rpm adjustment. A derailleur arm guides the belt up and down between these.
- It has vertical slots cut in it: it is 'segmented'. It is expandable! There is a conical wedge do-hicky on the motor spindle which can be pushed up and down, expanding or contracting the pulley diameter by a small amount. It's not visible on the video, but the pitch control pulley on the motor assembly is raising and lowering this conical wedge.