Is Powmaxx the same as Powmax (Leadman)? If so, I don't think you'll find any pots, just precision resistors (last color band is red or brown instead of gold) in their place. I don't think that precision resistors are used for anything in the PSU, else except the overvoltage circuit, but in my 300W Powmax this is handled by a single 8-pin chip that doesn't need any resistors.