Sir Haelind . . . . .
There is a HIGH probability, that optical interrupter unit is going to be good.
Instead, have you checked the changer for a broken or saggy loose rubber drive belts .
To test that unit, you can put it back where it can be pugged in, with its C401 connector, and get power to it again, but not necessarily being physically mounted in place again.
You would then want to power up and use your cell phones camera to view the slit that is on the C70 side that has an infrared light emitting diode within it and shoots out of the slit toward the IR phototransistor that is within the other 230 side of the unit. Now, is your cameras display screen showing the light output ?.
Since viewing its IR with the eye directly is not being possible.
An alternative test for the diode is to connect a DVM in its diode test mode and probe the diodes leads pads. It should read OPEN LINE in one test probes positions , and the foward voltage across the diode, when you reverse meter lead positions / polarities in the second test.( Or vice/versa . . .with there being that 50/50 chance, that you lucked out with that first attempt. )
If you find a good juction in one of the two polarity tests, the unit should be a good one.
Now, to test the photo transistor functioning, place the DVM in DC volts test mode use its probes to test and read across the two connections of the 230 half of the unit. Then take an opaque card and use it to alternatively block and unblock the light beam passage between the two halves slits.
A large voltage swing should be metered between either the blocked and the unblocked beam conditions.
Thaaaaassssit . . . . come back with your findings or for further operational / testing queries.
73's de Edd . . . . .
If at first you don't succeed, then try playing second base.