The voltage across the motor when playing is small, tens of millivolts, just enough to nudge the sled along.
What happens is this... the lens itself (not the sled) moves in a horizontal direction to cover tracking and to allow the beam to follow the spiral on the disc. The voltage on the lens is also fed to the sled motor servo. As the voltage on the lens coil gets larger (because the lens is moving more and more in one direction) the servo detects this and nudges the sled forward a fraction. The voltage on the lens coil then drops back to zero and the process repeats. So what you see is the sled shuffling along slowly.
So... if the player is playing music for this 30 seconds or so you mentioned, then you should be seeing an ever increasing voltage appear across the sled motor. If that is not happening (yet the disc is playing) then the problem sounds obscure and related to the servo circuitry.
What happens is this... the lens itself (not the sled) moves in a horizontal direction to cover tracking and to allow the beam to follow the spiral on the disc. The voltage on the lens is also fed to the sled motor servo. As the voltage on the lens coil gets larger (because the lens is moving more and more in one direction) the servo detects this and nudges the sled forward a fraction. The voltage on the lens coil then drops back to zero and the process repeats. So what you see is the sled shuffling along slowly.
So... if the player is playing music for this 30 seconds or so you mentioned, then you should be seeing an ever increasing voltage appear across the sled motor. If that is not happening (yet the disc is playing) then the problem sounds obscure and related to the servo circuitry.
That's a very unusual problem. The real definitive test is to monitor the voltage I mentioned (across the sled motor) and the only easy way is to tag two wires to it so that you can securely connect them to the meter and observe.
A sled motor should move with perhaps 100mv or so across it. If you are not seeing at least that (and the voltage rising and rising because the motor isn't moving) then there is a servo problem which is very unusual. If you do see the voltage then it could be just the motor that's "sticky" or lazy... it happens and its a common issue across many players.
You need to do that test though to actually confirm if voltage is there or not.
A sled motor should move with perhaps 100mv or so across it. If you are not seeing at least that (and the voltage rising and rising because the motor isn't moving) then there is a servo problem which is very unusual. If you do see the voltage then it could be just the motor that's "sticky" or lazy... it happens and its a common issue across many players.
You need to do that test though to actually confirm if voltage is there or not.
That sounds like a faulty or sticky motor. What might be worth a try... unsolder or unplug the motor (at least one lead must be isolated from the circuitry) and remove the belt so that it can't damage the teeth on the gears. Now connect a 9 volt battery across the motor for a few seconds, then reverse the polarity and do it again. That can clean up any carbon on the commutater and might go some way to seeing if the motor is faulty.
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