Bizarrely enough I was given a Philips DVD player (maybe a 622 or 922 - don't really know) by a colleague at work as it was broken, and I am actively looking for a box to hack into my home empeg dock. Its symptom was that it would never recognise discs.
After checking the electrics and realising that the laser and sensors appeared to be working, I thought I might as well mess with the mechanicals. 20 minutes later I scored a DVD player - eventual cost, a case of Budweiser, as he'd bought himself a new DVD expecting this to be a goner.
The issue boiled down to the fact that the head has no position sensor. It expects to start at a certain point, and then just times the motor. Very basic - and the rack & pinion had moved by a couple of pins. I just moved it to one end and tried each possible position until it worked (the boot sequence and time taken to change discs was the only reason it took as long as 20 minutes)
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Rory
MkIIa, blue lit buttons, memory upgrade, 1Tb in Subaru Forester STi
MkII, 240Gb in Mark Lord dock
MkII, 80Gb SSD in dock