The low-voltage stage translates mechanical dial adjustments into direct motor performance.
Monitors back-EMF feedback. When the lathe cutting tool bites into metal and slows the motor down, this circuit auto-adjusts the voltage to maintain consistent RPM under load. jymc220bi schematic 2021
For higher horsepower ratings, enlarging the heat sink area is recommended to maintain stability. Common Faults: For higher horsepower ratings, enlarging the heat sink
Before examining the circuit traces, it is helpful to look at the electrical limitations and rated performance of the 2021 production run: Specification Rating 220V - 230V AC (50/60 Hz) Output Voltage Range 0 to 180V DC (Pulse Width/Phase Shifted) Rated Continuous Current 6.0 A to 8.0 A Maximum Peak Current 12.0 A (Short burst/stall protection trigger) Compatibility For higher horsepower ratings
Faulty zero-start microswitch on the potentiometer, cracked solder joints on the high-wattage drop resistors, or a failed logic IC.