Sega CD Model 2 Repair Notes

From time to time I like to fire up my disc based systems to keep the grease viscous and make sure everything is in good working order.  Well last night I fired up my Model 2 Sega CD and discovered that all was not well.

The disk tried to spin up and this horrible grinding and scraping noise came from the drive.  After several attempts the disk finally loaded, but it was painful and I shut it off immediately to prevent damage.  I managed to do some damage getting the silly thing apart, but everything is back in working order now.

Problem: Grinding

The grinding noise from a Sega CD Model 2 is evidently a pretty common issue.  There's a laser limit switch which the system uses to tell that the laser assembly has reached the center of the CD spindle.  Over time this switch stops working as desired.  The switch is essentially just two thin strips of copper inside a plastic shell.  When the sled touches the switch, the two strips are supposed to make contact and inform the mechanism to stop the motor.  Most people seem to think this switch gets bent out of shape from repeated use, and they will gently "bend" it back into place so it begins working again.  While that definitely works, I believe oxidation is also a factor, so I also used a pipette to drop a dab of Deoxit into the switch for good measure. 

Solution

Gently bending the limit switch "forward" for a few seconds and applying a drop of Deoxit cured the grinding problem.

Problem: Scraping

After I got everything back together and got the drive spinning again, I noticed there was a persistent scraping/scuffing noise.  At first I thought this was some issue with the magnetic clamp on the drive door.  (There's a circular magnet on the door which helps to lock the CD in place when the door is closed).  With the top of the CD unit removed and the magnetic clamp attached independent of the door, everything seemed to work normally, however when I reassembled it, the scraping persisted.  I eventually noticed that if I held the unit upside down while it was reading the disc, that the noise disappeared.  Upon closer examination, the CD drive landing was almost flush with the disc well.  This was causing the disc to scrape the well.  I noticed too late it was scratching the disc - my copy of Ecco Tides of Time now has a ring scratched in it :( It was also causing the magnetic clamp to scrape inside its assembly.  The problem was caused by the four rubber shock dampening grommets that hold the CD drive in place.  They were simply too old and had mostly collapsed, causing the CD assembly to sit too low.  Since I could not find replacements for them, I did the next best thing and rigged it.  

Solution

I cut some crude plastic washers out of some large heat shrink tubing and placed them on top of each of the four shafts that hold the drive in place.  This gave the collapsed rubber grommets enough support to lift the drive correctly. When it was reassembled the drive plane was now sitting about 2mm above the disc well, giving the disc plenty of clearance to spin freely.  In hindsight, I think leaving a disc in the drive may have contributed to the collapse of the original grommets, so I would recommend leaving the disc drive empty when not in use.

Problem: Door Switch

I'm not sure if this one is self-inflicted or not, but when I got everything apart, the door switch was twisted.  My recommendation here is to always take the top of the unit off with the door open.  Doing so with the door closed means that the top is contacting the door switch as you're working it off.  The reason I'm not sure if I did this was because the bend looked old, if that makes any sense.  

Solution

I ended up removing the clear plastic cover of the door switch and gently bending everything back into place. (To remove the cover you need to use a thin tool like a small screwdriver shaft to press the back of the cover forward while you pull it up away from the board).  It took quite a lot of trial and error to get it bent back to working normally again, so, like I said, always take the top off with the door open.

Problem: The System says "Checking Disk" but the drive is lifeless

This happened sort of in the middle of all of the troubleshooting and taking apart and putting back together.  The short version of the story is that the "Checking Disk" message appears when the system cannot communicate with the drive.  About the only way to tell this is what's going on is that "Checking Disk" stays on the screen even when the door switch indicates that the drive door is open (so it shouldn't be checking anything).  It took me a little while to figure out what had happened, but the system was extremely dusty when I disassembled it.  Evidently a piece of fuzz had gotten into the connector and was preventing good contact.

Solution

I ended up blasting the ribbon connector slots on both the mainboard and the CD drive with Deoxit and allowing them to dry completely (about 5-10 minutes).  After reconnecting everything the system started telling me to close the drive door again - which meant it was talking to the CD drive again.