That machine has that motor for a reason. It's meant to auto adjust the angle of the mechanism when the option "diagnosis" is turned on. The position for the gear is auto detected during factory adjustments and then stored on the eeprom together with other configuration data. If the laser is not operating on it's original cog position it's because the PS2 suffered a mechanical shock or the laser in it is not the original laser.
Ok back on topic, you should take the PS2 apart completely. disconnect the motherboard block from the body, also the HDD bay. Then disconnect the ribbons from the motherboard. remobe the DVD drive assembly of the Ps2 body as well. the two ribbons have a black stripe painted in them in one side. That side connects to the DVD drive. Mount them correctly or else it won't read anything at all.
Mount the DVD drive back to the body and screw with the 2 screws. The flatcables should be visible on the other side of the PS2 body. replace the motherboard and connect the flatcables. At this point the PS2 must be working again. Replace the HDD bay and finish.
About the cog on V1/V2 PS2s it's configurated with a RS232C (COM PORT) cable and a special software (made by sony). The PC has total control over the PS2 DVD drive during this adjust.
SCPH-10000_GH-001 SCPH-15000_GH-003 SCPH-18000_GH-008 SCPH-30001_GH-005 SCPH-30000_GH-016(V4) SCPH-30001_GH-010(V4)
2xSCPH-10190, 2xSCPH-10350, 2xSCPH-10280
"**** j0 hackers!"
-Sjeep (As seen on TOXIC OS ELF...)