Dont think it can be done ( testing head ), I just had the problem with a bad head and burned up two main boards, before I changed the head and now seams fine. I have a SP-540V and the printhead fuses are on the bottom right hand side of the main board two white little fuses side by side and underneath two flat cables that plug into the board. I tested the fuses with a 110v tester, touch the top of both fuses and if one doesnt have voltage, its blown. mac media in chester NY was a great help and repaired the boards for me.