old Alpine 7903M headunit problems

[Kei]

My 7903 will not read discs for some bizzare reason. I have looked through this thread about another user with what sounds like the same issue. Since i already owned a functioning 7915M aswell (which has been in bits before) i knew that the cd-mech was virtually identical.





This was the only difference, so i swapped the boards over.


Now on testing the 7903, it loads the disc in fine and spins it. The laser assembly moves from the inner track right out to the edge and stops where it then decides to park and eject the disc. (i don't think the laser is emitting either) The laser assembly doesn't move back and if i reinsert the disc it doesn't even spin. I rebuilt the 7915 with the cd-mech from the 7903, just to test it and it actually works fine, better than the original too. This leads me to believe that there is something up with the laser control circuitry, however i am at a loss as to what.

The unit also has an aux in to allow a second alpine headunit to be connected however if i plug a device in the output is very quiet. If i increase the amplification on the input it will distort.

I've been having issues with various old alpine units as you can see by the collection. The 7385R has a dead preamp, the 7903M won't play cd's (nor line in) and the 7915M has an intermittent remote/antenna signal. The 7915 is the current workhorse with a separate amp-on switch.

[Kei]

Just noticed that if i shut off my bench supply to the headunit with the aux input still playing through, the volume jumps up to what it should be. The fade control seems to function on the aux to. I've tried applying +12v to the audio interrupt in and the brown/white wire (which pauses playback) to no avail.