Quick update - I figured out how to take off the carriage cover this morning, couldn't see an easy way to check if the wires were connected correctly (they're underneath a paper-like sleeve and didn't want to screw something up worse) but did wiggle them a bit. I then tried a test cut with the cover off and amazingly the pen went up and down! Put the cover back on and so far it seems to be working correctly. Very strange but hopefully problem solved. Thanks.