Bridgeport series 1 CNC mill cutting circles, intro and common transistor problems

Bridgeport series 1 cnc mill. Just bought this used mill and it's been almost a 1 to 1 ratio on maintenance vs usage. The transistor at first kept burning up then once I upgraded the transistors the fuses started to burn on the z axis and then finally it burns on every start. Will definitely upgrade retrofit this machine to mach 4, Centroid or paycnc. Since I don't have an "R" in my controls, 4 quarter arcs is the only way to do a full circle.
Also have not had problems this being an open loop steppers motors, they were so far very accurate and reliable. The machine tends to burn the transistors on start ups. Other then that very solid machine.