I think the TT81 differs from the TT101 in that the latter TT has external buttons to increase or decrease rotational speed in small, regular increments. The TT81 does not have that feature, so far as I know, but as you say there are likely to be potentiometers internally that do modulate speed. As I understand it, adjusting such variables is part of what it takes to calibrate a DD. The servo mechanism was also described by JVC as being "bi-directional". My TT101 had the following issue when I bought it: At start up, the TT would come up to speed, but in the speed display window, an erroneous readout would appear, for example if set for 33, the digital speed readout would show "33.32" or "33.34". It would go on this way for a minute or so, and then it would stop dead. The brake would not actuate to stop the platter. The digital readout would disappear leaving only a decimal point lit up, and the platter would coast to a stop. What’s worse, the problem was intermittent but frequent. Bill Thalmann could not reproduce the failure mode in his shop. Nor could one other repair shop to which I sent the unit. Finally, I fiddled around with it enough that I made the intermittent problem into a regular occurrence. (Which is to say, although I had no idea of the real problem, I made things worse with whatever I did do.) I then found out about JP Jones and sent the unit to him. He had never worked on a JVC DD prior to working on my TT101. He found the problem described above; the PCB had cracked across a tracing which defect was hidden under a blob of solder. Apparently the JVC PCBs are hygroscopic. They absorb water from the atmosphere, swell up, and can thus damage a tracing. Once discovered, this was an easy repair. Since then I have found the TT101, with beefed up plinth and specially fabricated aluminum tonearm mount board, to be a superb TT.
Someone that can recap/refurbish/recalibrate a direct drive turntable motor?
My daily driver is a JVC TT-81 in the dual tonearm JVC plinth, but lately it's been pretty flaky, e.g. noticeable flutter, along with an occasional speed runaway and strobe not reporting correctly even though the speed is clearly close. Pretty sure it's never had service so I'm looking for someone to do the work. I scoured the forums and only came up with one place (Fidelis Analog) that appears to be currently in business. Bill Thalmann used to be The Guy but Music Technology looks to be out of business now.
Does anyone here know of shops that still do this kind of work?