Post by czroe on Dec 28, 2020 13:08:58 GMT
I bought a broken Turbografx-CD drive knowing that it was more than your typical bad gear since the listing showed the laser lit up with no disc and a laser unit that doesn't move/home:
www.ebay.com/itm/NEC-Turbografx-cd-rom-drive-parts-or-repair-/114578947781?_trksid=p2349624.m46890.l49292
Normally the laser will not light up until the unit homes to the center, trips the limit switch, then backs off the switch. That's when the lens will bob and attempt to focus and the disc might spin. If it isn't homing it obviously should not be lighting up, so I knew it wasn't going to be as simple as replacing the gear. Even knowing that, I have enough parts to completely replace the internals so I took the risk.
I received it and the laser unit was sliding freely without ratcheting along the worm gear as it normally would. Turns out the springy teeth that follow the worm gear were broken and the spring plate they attach to was bent back. The plastic base it all mounts to was also broken and missing the protrusion that actuates the homing limit switch, though that does not explain why the laser is lighting without homing.
I replaced the plastic base, spring plate, and follower gear/teeth with spare parts and checked the limit switch, which was fine. Of course, the central gear that typically needs replacement was broken in half so I replaced it. I found and removed broken bits from the replaced parts, like the other half of the broken gear, the limit switch actuator, the missing follower teeth, and some plastic bits that broke off the adjustment pots (those always seem to be cracked).
I still didn't have an explanation for the laser but I had replaced everything that was visibly damagaed so it was time to test again:
youtu.be/V5AObqLk86Y
I bypassed the lid sensor to observe the laser behavior and it never budges. It doesn't home or bob but the lense does light up. Strangely, it stays lit even after you hit Stop and all the drive appears to be powered down. You have to remove all power to get the laser to turn off. Since I can only see the IR laser through my cellphone camera I'm hoping I didn't look into it when I thought the thing was off.
Anyway, I'm ready to start swapping more parts but I thought I'd ask here first in case others have seen this issue before. I don't want to stick a good laser into it if it's a known issue that could damage other parts. Thanks!
www.ebay.com/itm/NEC-Turbografx-cd-rom-drive-parts-or-repair-/114578947781?_trksid=p2349624.m46890.l49292
Normally the laser will not light up until the unit homes to the center, trips the limit switch, then backs off the switch. That's when the lens will bob and attempt to focus and the disc might spin. If it isn't homing it obviously should not be lighting up, so I knew it wasn't going to be as simple as replacing the gear. Even knowing that, I have enough parts to completely replace the internals so I took the risk.
I received it and the laser unit was sliding freely without ratcheting along the worm gear as it normally would. Turns out the springy teeth that follow the worm gear were broken and the spring plate they attach to was bent back. The plastic base it all mounts to was also broken and missing the protrusion that actuates the homing limit switch, though that does not explain why the laser is lighting without homing.
I replaced the plastic base, spring plate, and follower gear/teeth with spare parts and checked the limit switch, which was fine. Of course, the central gear that typically needs replacement was broken in half so I replaced it. I found and removed broken bits from the replaced parts, like the other half of the broken gear, the limit switch actuator, the missing follower teeth, and some plastic bits that broke off the adjustment pots (those always seem to be cracked).
I still didn't have an explanation for the laser but I had replaced everything that was visibly damagaed so it was time to test again:
youtu.be/V5AObqLk86Y
I bypassed the lid sensor to observe the laser behavior and it never budges. It doesn't home or bob but the lense does light up. Strangely, it stays lit even after you hit Stop and all the drive appears to be powered down. You have to remove all power to get the laser to turn off. Since I can only see the IR laser through my cellphone camera I'm hoping I didn't look into it when I thought the thing was off.
Anyway, I'm ready to start swapping more parts but I thought I'd ask here first in case others have seen this issue before. I don't want to stick a good laser into it if it's a known issue that could damage other parts. Thanks!