Havn't done it myself, I came across the info when researching data on the stacker in my wagon on the net.
It seems to be a problem with Alpine 6 stackers, sometimes they lose the cog alignment when feeding a disc into the laser pickup.
The people that had the balls to open up the stacker had success in repairing the fault, so it must be fairly simple.
If you are mechanically minded give it a go, you would have to take it to the audio tech any way, this way at least he will earn his money