Also, there is the possibility of a bad motor driver. This is not always an IC. It oculd be just a ocuple of transistors. If the spindle motor starts pulling too much current it can blow the driver. If in doubt, follow it back to whatever drives the motor to see if it is getitng dsrive but not driving. In that case the spindle motor might be bad.

The circuit is usually simple as hell. It is off when the buffer is almost full and on when the buffer is almost empty. And a transistor maybe for braking, if it even has that it usually just shorts out the motor so to load it and stop the disc. They don't use a negative voltage usually they just calculate the mass of the disk and with the motor loaded by the short it must stop ithin a certain time.

You say it is a combo unit ? Expect the absolute cheapest of circuitry. In fact if it has a pop up door instead of a drawer it probably has no braking and just has one transistor to drive the motor, on or off. Might even be a DTC something because the current is low.

Or supposed to be.

If you can get a print and find the FOK line and check it that is fine, but if whatever drives that motor is not told to turn on you can pretty much assume you don't have it.

I would clean the laser. what's more if you clean the laser and it starts working, tap on it with a screwdriver handle or something and see if it skips easily. then you got a weak laser. It will work for a time, BUT it is regulated so it will not last.

If you decide to tweak up the laser power ith that little pot, remember it is not going to last long and probably will still skip easily until it fails.

It is nice practice probaably fixing those thihgs but you are not goiung to make a fortune at it. Also, in some cases you can get the whole CD drive for about the cost of the laser. (I had a bad new one once and had to frankenstein the damn thing between parts from the new and old because the job had to go out, piece of ****)