Get a service manual on your engine. May be as simple as a blown fuse to the trim drive, or a bad trim switch if you only have one. If you have an up and down relay, swapping them helps sometimes if one is bad......in your case you swap the up and the down, and then the engine will drive up but won't drive back down.....bingo....smoking gun...the relay, or your fluid reservoir is low or empty, or your motor is bad.........