JaS wrote:I'd check that all speeds work, are stable and that it starts/stops/changes speed very quickly. If the platter takes more than a second to stop it may have had the brake disengaged/removed (the mechanical brake is solenoid operated so expect a little 'thunk' noise when pressing stop).
When running it should be very quiet, but a worn/damaged/badly adjusted brake belt can cause 'rubbing' noises when spinning.
Old transformers can become noisy so I'd listen for excessive 'buzzing' from the power supply.
The main bearing is durable, but if it's been transported without the clamp, or with the platter attached there's a small possibility of damage. There shouldn't be any lateral play in the bearing, or any noise when running. It's worth adding a drop of oil straight away if you buy it.
Short of stripping down the main bearing or getting an oscilloscope on the main board, I can't think of anything else? I've had one with a noisy brake and blown strobe bulb, but otherwise they are very reliable IME.
Re buzzing transformer, I had this issue with my sp10mk2. Problem was fixed by replacing caps in the psu. Actually unless you are sure the psu caps have been replaced recently I would change them right away as a couple of the psu caps are prone to failing. Two failed on mine fortunately no damage to the turntable was done.