Hello, today I obtained a Giant Butte (probably too may sweets)Lol. The shifters are Shimano Total Integration, they have two paddles one for shifting up and the smaller one for shifting back down. When shifting, up, the front derailleur, it does move the chain to the larger chain rings but as soon as I let go of the larger paddle, the derailleur goes back down and does not stay in position. I feel the problem is in the shifter and not the derailleur. I am hoping someone here can explain how to disassemble the shifter and what to look for inside the shifter and if it is something that is repairable. Thank you