回答“Mighty Mouse doesn't scroll down”I would like to add my answer as I don’t see it yet. If you follow the link to the disassembly instructions or if you have taken the mouse apart already, you will see that there is a metal tab that is near each of the black magnets on the rollers . This is there to measure the resistance difference of the magnets so it knows that the roller is moving. In my case, the tab was physically touching the ‘down’ roller. Well, if there is no gap, then the mouse cannot tell if that roller is moving. TLDR: make sure the metal tabs next to the black wheels on the roller bars are not touching the black wheels. If they are, simply bend them back slightly.