Are you sure the limit switch is good or that it has an uninterrupted
connection to the player electronics? Did you try measuring continuity of both
sides of the switch to determine it's condition? The continuity for each side
of the switch when closed must read infinity with no resistance. Also, are you
sure there's only one limit switch?

Another thing you could do is to trace the motor wiring and the open/close
control to specific traces on the player circuits. This might help you to find
parts that could be suspect on the circuit path that the parts are connected
to.

Also I checked the voltage on another Philips (different model) CD
player. It gets -5V immediately after pressing the OPEN switch on the
front. This causes the motor to run in the other direction to open the
drawer.

If this CD player uses the same chassis and possibly even similar electronics
despite being a different model, it is still possible that the functional
player might provide clues as to what is going on with the broken player.
Although schematics would still be most helpful, you can use parts from the
good player to compare the values of suspected parts on the bad player. -
Reinhart