most cdrom laser diodes have 3 pins one is comun to the laser diode and to the photodiode is easy to find the photodiode .Just shine some light into it and with a tester check if that affects the reading ..then you would have found the opto transitor or photodiode ,.the other reamining lead is the laser .. But these lasers are no visible .So don't look into it if you apply volatge **broken link removed**