Sega CD Model 1 Repair...

[Oldskool]

What I do when the system is apart is manually raise the cd mech and lock it, then put the disc on and the top magnetic part and see if the system will boot up and the game will play. This way I know the laser is still fully functional before proceeding to repair the crazy mechanical parts.

Yup, what you said. Also take a look at the limit switches and make sure they are in the proper positions after you manually set the disc before you turn on the console.

I always recommend a new belt too. It can cause all sorts of odd things to happen, the most common one is that it will eject the cd as soon as you put it in. Just because the belt looks ok doesn't mean that it is. They get stretched and have a difficult time raising up the laser assembly. Although, technically if you manually set the disc/laser assembly into the proper position you are basically doing the work of the belt. So for testing purposes it's not needed much.

Another thing - people worry too much about the aligning of the gears. They are engineered so that if they are out of place they somehow always end up back in the same position. I noticed this after trying to adjust gears for hours and hours, they always seemed to reset back to a default position. I think this is an engineered fail safe so that if the gear ever slips the console can set their positions. It achieves this when the laser assembly has been fully raised the gear will keep turning until it hits the stop on it. Of course if you have a worn belt it will not raise the laser assembly all the way up which will make you think it's the gears. Rather than wasting time with the gears (that are rarely ever actually broken) focus on the belt, the laser assembly hinges and the limit switches.

Again, it's very difficult to figure out through a forum. The part that confuses people the most I think is the tray and the gears. You just have to turn every thing and see what does what. Once you gain an understanding of how it all works you will figure out the problem. And because everyone is always talking about the gears, don't let that fool you into straying from other more simpler issues.