VPI Scout - slow speed , help ?

It won't so much be voltage that will cause your problems, (if it is a electric source problem) it will be line frequency varying.

While the VPI SDS can vary, and ramp down voltage, the Platter speed is set by varying the output frequency of the SDS.

While not impossible, it is rare that line frequency will vary that greatly to cause you a considerable slow condition one time, and then run fast another.

And I sort of doubt your KAB Strobe Disc is at fault.

I assume your Scout uses the newer style Inverted Bearing.
These are to be lubricated with grease, not oil. A simple Lithium Grease will be suitable.

I suspect your problem to be your conditioner. Plug direct to the wall, not the power conditioner, and then take a measurement with the Disc. If you have the stepped Motor Pulley (the one with a number of ridges on it), you can then set the belt upon the ridge-groove of choice to get as close to 33-1/3rpm as you can.
Hope this helps. Mark

At least for now, you are up, and running.

Pretty much all of us, have been drawing straws as to what your issues were, and I guess all we could do is make suggestions. When problems such as these arise, one must hold every component of the drive system suspect. And then methodically check each.

While I'm not sure of this, because I have no experience with the 300rpm motors VPI uses, so I am not sure if the Motor Run Capacitor is typically the same value for either 600rpm, or 300rpm Motor?

Thos are perhaps questions others here can answer, or VPI?

There were a few unknowns about your situation, whether the Table was bought like this, or did you make the 300rpm Motor swap recently yourself, or? I'm getting the impression you may have bought the 300rpm Motor used?

That there was either A., a problem with the Motor itself, and you bought a bad one? Or B, that this Motor requires a different Run Capacitor, which was typically included in the purchase when gotten new from VPIm but you didn;t get included with the purchase? Mark