From standby (red light), inserting a disk does turn the PS3 on. Motor does not engage to take disk though.
One thing I've noticed with the drive, it's similar to the CECH-2503 drive but the sensor PCB is a KBL-001 while the CECH-2503 is a BL1-011. Maybe there is a fault with it that can cause this problem in the CECH-3003 but not when the drive is used in a CECH-2503? Just an uneducated long shot idea, it's all I've got! lol