do an encoder strip check..you have to goto service mode though to do. and see how far the numbers are when you do the test. I should not be that far off. if its why off then it might be the encoder strip. I would check test and the spring that the encoder strip is on..My would assume that it is the encoder strip. will probably need replaced. not hard to change. do the test first. and see.
Hope this helps
Hope this helps