EMPLOYEE WAS TROUBLE-SHOOTING AN ELECTRICAL PROBLEM ON A 637E CATIPILLAR PAN. HE WAS IN THE SHOP AT THE PREP PLANT. WHILE DISMOUNTING THE PAN HE TURNED HIS LEFT ANKLE. FLOOR WAS LEVEL, SMOOTH CONCRETE WITH NO HOLES OR OBSTRUCTIONS IN AREA. EMPLOYEE STATED HE DID NOT JUMP AND USED PROPER DISMOUNTING TECHNIQUES.