When your carriage stops at an unexpected place on its travels up and down the rail, get out a flashlight and take a close look at your encoder strip - that's the silver strip that runs through the back of your carriage. The encoder strip tells your carriage where it is on the trip from left to right. If there's a bad spot or a dirty spot your carriage may stop at someplace other than the end cover where it is normally housed at rest. The photo shows two pieces of encoder. The piece on the left is worn out, de-laminated. The one on the right is fine. The "clear" portion of the strip has a zillion tiny lines that mark every millimeter of the space from left to right. They are easy to replace and they don't cost much...usually less than $30.
Cleaning note: While we are on the subject, do NOT clean your encoder strip with alcohol or window cleaner or anything but water and a very soft cloth, like an old t-shirt. If the fabric comes back with black marks on it, stop cleaning...as your encoder strip doesn't get cleaner than that. The black is tarnish from the silver. Dampen the soft fabric with warm water and wipe it lightly on both sides of the strip from the far left to the far right. Now use another piece of soft cloth that is dry to very gently wipe the strip of water droplets and water marks. Now you are done. Do NOT do more. If the encoder strip gets sticky or gummy you may as well order a new one as it is probably not going to work well and may already be a problem.
Cleaning note: While we are on the subject, do NOT clean your encoder strip with alcohol or window cleaner or anything but water and a very soft cloth, like an old t-shirt. If the fabric comes back with black marks on it, stop cleaning...as your encoder strip doesn't get cleaner than that. The black is tarnish from the silver. Dampen the soft fabric with warm water and wipe it lightly on both sides of the strip from the far left to the far right. Now use another piece of soft cloth that is dry to very gently wipe the strip of water droplets and water marks. Now you are done. Do NOT do more. If the encoder strip gets sticky or gummy you may as well order a new one as it is probably not going to work well and may already be a problem.