Musical Fidelity DVD1 wont read any discs

I have one unit in-it will start a search routine (the laser head will try to focus up/down)but will not read any disk at all. The system hangs.
I Have tried new transport ,laser etc,Replaced the RF chip (TZA1033HL) on the transport pcb, still not reading anything.
Does anyone have any pointers, schematics??
How can we tell if the laser is actually getting a voltage and turning on?
This unit uses the Phillips VAL1201-01 Transport which I imagine is/ was used in allot of DVD players...
Around 2001.