Sega CD Model 1 stuck on BIOS screen

I recently picked up a non working SCD model 1 that didn't power up. It needed a fuse which I replaced. Now it powers up and gets stuck on the BIOS screen with no sound or animation. After searching the forums it looks like it might be an issue between the CPU and RAM. The original SMD caps on the main board were bad (corrosion on the ground rail) but either the original owner cleaned up the board or it just wasn't that bad because the board looks fine (the ground rail corrosion was the only indication they were bad) . The only chip with any corrosion on the legs was the boot rom (IC4) and I verified that all the legs had continuity. I replaced the SMD caps and the problem remains. The other thing I noticed is that initially the laser lens was in the center and when I push it out to the edge, it doesn't return to center upon powering up. Should that return to center regardless of the boot status?

I cleaned the edge connectors and verified that none of the cartridge pins were touching. I checked the voltages going from the sub board to the main board and I get +5V and +11V (VCC2 I think).

Where do I go from here?

 

A model 1 will do this if there is a problem between the drive and the rest of the system check near the drive ribbon cable.

 

So I verified that the connector on the mainboard to the drive has continuity on all its pins. And I verified continuity on the ribbon cable itself. When powering up or off the Genesis, I do see that the laser eye bounces a little, so it is getting some small amount of power. But the sled still doesn't move back to center.

 

Let me know if you ever solve this, I have one too unfortunately.

 

If you push the laser lens out to the edge and then power it on, does it return to center?

 

You did the caps on the power/soundboard to right?

 

I didn't do the caps on the sub-board. I do get the BIOS screen to show up and I can also get the Genesis cartridges to play audio through the SCD audio jacks. That led me to believe the power board was ok.

 

Might be and you may have the right hunch on the CPU-RAM issue. However. The electrolytics on the subboard is crap! I have hade two model1s that behaved really bad with bad caps on the sub board.

One i managed to revive (only got to the bios at first, played the music but no menu) and the other have no sound, guess its a missing track under an amp or something.

 

I just watched a video of someone fixing a Model 1 and noticed that even without the Genesis powered up, if he puts power to the CD part, it will move the laser and tray back to home. That means I either have a problem with power to the drive, or with the drive itself. I'm a bit more hopeful now.

 

Well I got a bit further. If I spin the big black gear to lower the lens, pull out the tray, and then power up the Genesis, it will pull the tray back in. It will move the tray up, but it will not move the laser lens back to center. And I still don't get any further then the frozen BIOS screen. I guess that means the drive is getting power. Not sure why it won't move the lens to center though.

 

Success! Almost. Found a broken trace on the edge connector to the UWR line on IC2 and patched it. Now I get the BIOS screen and everything. But now when I insert a disc, it spits it right back out. That seems to be a more common fixable problem, but at least I'm making progress.

 

If I can get the tray to lift the disc, the game starts playing. And even after powering it off and on again, the game loads up fine. But when I eject it and try a different game, it ejects the tray again. When the tray does close, I can hear a motor spinning right before it ejects. Weak belt?

 

If you dont have a belt replacement at hand, you can use those small hair bands made in silicone. I found some in my wifes couboard and they strech just the right amount and works a sharme.

Also polishing and bending the end of stroke switches might be a good idea.

And as a word of causion, dont lose the small plastic plunger when aligning the sled. Wont work without it.

Glad to hear you got it working! Awsome!

 

All fixed! A new belt fixed the tray issue. So all in all, a new fuse, mainboard caps, one broken trace, a new belt, and lots of hours of troubleshooting. But it looks great under my Model 1 Genesis. Thanks for everyone's advice!