I'm repairing power tools and need to know how these switches function because there is a PCB inside , it's obviously not just a simple switch. I also need to know a test procedure with a multimeter to know if it's good or faulty.

 

Based on no description at all, a reasonable guess is that the four terminals are a switch for reversing rotation. The two screw terminals would be the main power switch. but with no hint as to if the control is variable speed or not, there is no simple test with a multimeter to check an AC power variable speed control.

Without more information that is about all you can hope for. A continuity test can quickly see if the direction switch is OK or not.

 

Based on no description at all, a reasonable guess is that the four terminals are a switch for reversing rotation. The two screw terminals would be the main power switch. but with no hint as to if the control is variable speed or not, there is no simple test with a multimeter to check an AC power variable speed control.

Without more information that is about all you can hope for. A continuity test can quickly see if the direction switch is OK or not.

These are fitted to grinders so no reversing , the four terminals are two to the stator and two to a capacitor.

 

OK, No reversing! Does the grinder have a variable speed?? or two speeds?? My old MILWAUKEE grinder has a brush motor with only one speed, which is real fast. Likewise my Harbor Freight grinder. Similar functions, opposite ends of the price spectrum.