Belt might need replacing. I always give the platter on my SOTA a nudge to get it up to speed quickly and to help spare the belt and motor extra strain.
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Your Sota should be up to speed in less than one revolution. Replace the belt first and clean the pulley and platter. Beyond that it could be a motor or power supply problem. There's a 220 microFarad capacitor on the circuit board that starts the motor. It's easy to replace if you are handy with a soldering iron.
I used the supplied strobe disc with my Sota to measure the time it took for the bars on the disc to stabilize. If the platter gets up to speed in exactly one rotation from zero then it would take 3.6 seconds for the bars on the disc to stabilize after turning on the motor. Use the strobe disc to measure yours.
We had these discussions on another thread. Search speed control and torque. If I recall correctly, someone's DD tt gets up to speed in a quarter rotation.
I have an early version Sapphire, ca. 1983, which uses a servo motor. Later versions, or at least most later versions, use a synchronous motor, as I understand it.
I haven't taken the time to dig out my strobe disc, but based on a quick look my Sapphire completes the first revolution in almost exactly the 3.6 seconds Tony cited (I was going to say a tick under 4 seconds before seeing his post). It appears to be nearly up to speed at that point, although perhaps a fraction of a second away from getting all the way there.
33.3 rpm is about 1.8 seconds per revolution. How do you come up with 3.6 seconds for the bars to stablilize equaling being up to speed in one rotation. I havent bothered to actually try the strobe thing, but it takes me more than one revolution to cue up a record anyway, so its not really an issue on my Cosmos.
Hi Manitunc, since the platter is starting from 0 and assuming linear acceleration and that the platter reaches 33 1/3 rpm at exactly one revolution, then the average speed of that first rotation is 16 2/3 rpm. After the first rotation the average speed will be 33 1/3 rpm. I'm sure your most excellent Cosmos does better than 3.6 seconds if the belt is in good condition.