Arcam Alpha (one?) had a Philips CDM4 mechanism.
general problems with Philips mechanisms are the belt that drives the loading mechanism.
It is situated on the right of the loading bay (easy to see).
The belt has either 'formed' and slips at certain spots or stretched too much and can operate the tray but doesn't have enough power to lift the CD mechanism.
Another problem usually associated with Philips mechanisms that haven't been used much is a faulty spindle motor.
Doesn't read TOC or doesn't play.
Sometimes this can be checked by sortof very gently 'breaking' the spinning action of the disc with your finger tip.
Means replacement of the mechanism.
Another common problem is the laser mechanism itself.
If you know the right point the laser can be adjusted with 1 of the 2 pots at the rear of the mechanism.
I thought a certain resistor voltage must be adjusted to 50mV.
Would have to look in old manuals for that.
The other pot is focus offset and must be kept untouched.
if adjustment doesn't help replacement is all that remains.
These 3 things can cause these problems.
Given the troubles the belt seems the most likely.
Easy to cure as well.
If it is stretched you can 'shrink' it a bit ( is a temporarely measure at best ) by holding the belt over a flame, heating it but make sure it doesn't 'smoke'.
Make sure it doesn't catch fire also
and the whole belt must be 'processed'.
replacement is best option.
Another way to shrink a stretched belt (if not too badly stretched and still has some sturdy stretch in it) is cutting it in 2 and cutting off a tiny bit at one end (shortening it slightly).
Glue it together again with super glue.
As one spindle is small in the mechanism (motor side) this may not work optimally in this case or break at the glue point if too much glue is used.