So what shot is making this happen exactly? You just say "back of the machine". What shot specifically?

Do you have the manual for it? Maybe it's missing a post or rubber that should be blocking that area?

Can you post a photo of where it is getting stuck?

Reading his description a few times over. Maybe he is talking about the saucer on the blanka shot?

If youre shooting the blanka shot and its ending up there, your machine is missing guide or posts or both.

Yeah - that definitely shouldn't happen from the Blanka shot.

Both the left and right ramps should raise and lower. If that's not happening there is an issue. Both of the ramps use fuse F25, so if neither of them work I would start with checking the fuse. Can you lift the left ramp manually, is it seized? Solenoid 7 runs the left stargate ramp, you can try it in the machine's test menu to see if it is working. If it's not working in the test I would check the solenoid to see if a wire is broken or anything else obvious, like the linkage to the ramp is broken. With all that being said if you are shooting the Blanka shot and it is ending up under the left ramp you are missing a piece somewhere because that shouldn't happen.

Good luck.

Here is a picture of what the guides under the left ramp should look like. If you slide the playfield forward you should be able to look through the back corner and see if they are missing or bent.
StreetFighterGuides (resized).jpg