Sega CD Model 2 Repair Notes

By samson7point1
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.

Comments

Post a Comment

Popular posts from this blog

What I've Learned Fixing Optical Drives

By samson7point1
So You Want to Fix an Optical Drive If you found this page looking for advice on how to fix an optical drive, you might be in luck.  There's a lot of information and prognostication out there these days that might tell you fixing a laser mechanism is a losing proposition, but the fact is that in many cases these drives are completely fixable. Over the past decade I've begun fixing a optical drive failures in a wide variety of hardware. In the process I've learned a thing or two about a thing or two and I've compiled my findings here in the hopes they may help someone else. Full disclosure: I'm a technical professional, just not in the field of electrical engineering.  I do this as a hobby.  My skills and information comes from a lifetime of curiosity and decades of reading manuals, reading books, learning from experts and practical application. My success rate in repairing these drives and restoring them to original function seems to be in direct opposition to popul
Read more

FM Towns PC ODE - Grey Tower Wizard Installation Notes And Review

By samson7point1
Image
The Gray Tower Wizard is an Optical Drive Emulator (ODE) for FM Towns PCs, not to be confused with the FM Towns Marty (which is a stripped-down and consolized version of the PCs) or the Doc Brown ODE for Marty (which is made by the same person).  The FM Towns PCs have dual floppy drives and the ability to add RAM which makes them capable of running more complex or resource-heavy games than the Marty. How Do You Get One? The kit including shipping ran me 150 Euro.  Ordering one is basically the same process as the GDEmu, Rhea, Phoebe and Doc Brown.  I had never ordered anything from Deunan before but I'm more than familiar with the popular complaints about it being difficult.  It's not like ordering something from Amazon, but I didn't find it to be very difficult at all.   I signed up for blog updates, waited until he announced he was going to sell them, then refreshed the Wizard Ordering page  until he activated it.  When he did, the ordering page changed to a form to submi
Read more

ColecoVision RGB Mod [Updated]

By samson7point1
Image
[Updated June 2020]  As with all hobbies these things can be learning processes. After initially completing this mod, I discovered some new things and made some changes.  Primarily, I've re-incorporated the RF box for actual composite video, figured out the black & white picture problem, added a buffering capacitor to the audio output and tapped the audio from a different location to maintain compatibility with the ColecoVision Expansion Module #1.  The Expansion module doesn't work with RGB out, but now it's at least usable with composite Genesis 2 cables.  Background ColecoVision wasn't something I had or even played growing up, but several years ago someone gave me one.  Since its only AV output is RF and that makes it hard to have multiple systems connected at once, it sat in a box for about 10 years until I stumbled across Ben Heck's tutorial on a very straightforward composite video mod. The Picture Quality Produced by the Ben Heck composite vide
Read more