After every use, unplug the saw, clean sawdust from it's air vents, and clean any grease or oil from the cord. If the motor stops or smokes or sparks excessively, first check the brushes, then test the switch, motor, and power cord for electrical faults. Always let the blade reach its operating speed before bringing it into contact with the work. Brush replacement is a common repair chore. Although a brush will operate satisfactorily until it is just about worn away, it is best to replace it before this happens, otherwise the communtator may get damaged.
Brushes are blocks of a soft carbon material much like a lead pencil.
As a rule of thumb, replace brushes when they are shorter than they are wide. Always replace both brushes. Besides wearing out, brushes may stick in the housing. Remove both brush housings. Examine the brushes, springs, and housings.