Turntable Advice?

Apparently my post of an hour or two ago never made it. What I said then was that the term “three phase DC synchronous motor” is an oxymoron, because DC has no phases by definition.  DC motors that do operate off AC convert AC to DC within the body of the motor. What is probably going on is that the phoenix derived controller operates on the AC side, thereby controlling the DC motor. Also, a stock TNT may well be superior to an original Star Sapphire but all bets are off if the SOTA has the Eclipse mod, in my opinion of course. I wouldn’t arm wrestle over it.

I believe we’re talking about 3 phase AC, not DC. The Phoenix design is for driving 3 phase AC. I think the old SOTA motor might be DC type.

The original electronics used a feedback system to check platter speed.  Sounds like something with the feedback or servo is broken.  Probably your motor is OK, but if SOTA recommends a new motor to go with the Phoenix electronics, I cannot over-state the benefits to be derived from letting them do it. You'll be amazed.

Funny story: about 25-30 years ago, when SOTA first came upon the scene, they offered a turntable as a kit.  A friend of mine who was a very capable engineer decided to build the kit.  When he got the turntable completed, I was invited for its maiden voyage.  The object was just to see if it worked. We sat across from each other at a table upon which the SOTA was supported.  He pressed the start button, and at first we were both pleased to see the platter start to rotate and quickly reach what was apparently the correct 33 rpm.  However, it didn't stop there; it continued to accelerate, faster and faster until I thought it was starting to rise up on the spindle, and I feared it would literally take off and hit one of us. I thought seriously about ducking under the table for protection. Fortunately, at that point he cut the power, and we both started laughing.  He had miswired that servo feedback loop.

Just to be clear, although I did use the words “repair your turntable”, I was not implying that the OP should actually do the work himself. I went on to suggest he send it to SOTA for the Phoenix upgrades and a new motor, if a new motor is even needed. SOTA can advise on the condition of the motor itself. They may even have upgraded the motor in connection with their adoption of the Phoenix electronics, since the latter is designed to drive a 3-phase AC synchronous type.

What tomwh said.  Repair your turntable and add the Phoenix controller system.  It will be a huge upgrade, in my opinion, because, in my opinion, a major issue with the old Sota Sapphire was speed stability.  I owned one for 10 years before figuring that out.  Also, you say the motor has "gone bonkers".  Can you explain further?  If the motor still operates but speed is very inaccurate (I mean beyond the slight wavering of pitch), then the problem may lie in the electronics that control the motor, not in the motor per se.  That would be a win/win for you, if you send it to Sota.  They could repair the problem by installing the Phoenix designed controller in place of the original electronics.  Also, by all means keep the SME V vs any of the tonearms that come with the mediocre turntables you listed.  And finally, get a new cartridge if that would please you, or don't. That part is icing on the cake.