To weld aluminum the torch has to be positive polarity and earth return negitive pure argon gas or boc alushield must be used.Best to use a teflon liner,aluminum mig wire push the torch forward when welding .
Welder repairs norris we all had to start somewhere,try to obtain a broken set it is not always possible to get circuit diagrams for all sets,eye ball mark 1first then input and output voltages .best of luck