First a few questions and then a few notes:
Q
1/ You say the laser is OK, how do you know that?
2/ Does the disc start to turn?
3/ If it is turning is there a lot of servo action (noise) before it stops?
Notes:
Normally before the disc will start to turn the laser must establish a focus condition sometimes indicated on a FOK test point somewhere on the pcb. Watch the focus servo action when switching on the unit without a CD. There should be an up-down movement of the lens assy as it is trying to establish focus. It will try 3-5 times before shutting down.
Once focus is established the servo motor spins the disc up in a un-locked state until the speed servo can achieve lock. If this is impossible you often get the run-away speed symptom followed with a shut-down.
It is also important to see that the optical servo is balanced and not stuck in one extreme position, indicating a failure in one of these servo circuits. It must be able to move up-down and side-side while operating to track and maintain lock.
Correct operation of the laser is only possible by measuring the voltage drop over the current sensing resistor and verifying that it is near the current rating printed on most optical pickup assy's. The other method is to use a laser power meter. In a darkened room you may see the faint glow of the laser but that won't tell if it is working correctly.
NEVER LOOK INTO THE LASER DIRECTLY AT A CLOSE DISTANCE!
Look at this link for more tips
https://www.repairfaq.org/sam/
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