Silent electric motor to drive turntable.

[David Aungier]

Have you considered a microwave oven turntable mechanism with further reduction (if necessary) by belts and pulleys?

Interestingly enough Alec, the speed of microwave tables is about what I'd be looking for.

 

[David Aungier]

If using the 1:1 ratio like that, you may need quite a bit of power to rotate 200lbs and also stop it precisely at the 90° point.
If it has a vertical shaft and bearing below the table, one method to reduce friction is to place a large ball bearing below at the bottom of the shaft to support it, i.e. reduce the pivot point area.
I once did an interesting 300lb T.T. project that used an air bearing, the whole table is lifted with compressed air before rotation.Very friction free.!!
M.

The TT I am using has a nylon pivot bush/bearing and sits on radial rollers and it seems to work ok. The degrees of rotation arn't that critical.

 

[WHONOES]

Sorry, forgot to add link to post #7. It explains all about how to make gears much quieter by selecting the correct type.
https://khkgears.net/new/gear_knowledge/gear_technical_reference/how_to_reduce_gear_noise.html
Also, using a gear train would give a form of braking by shunting the drive motor.