The Comparator is used as a zero-speed sensor, Tach loss detector, overspeed sensor, and field loss protection relay. The relay is energized in normal running, if an error signal occurs that exceeds the the trip point the relay is dropped. the trip signal is 40 millivolts. You can check and adjust this on the board using an ohm meter. Common and the + trip point should read 4vdc. Adjust the trip pot cw till you reach 4vdc, or slightly higher to eliminate nuisance trips. The most common causes for trips are, the accel/deccel board adjustment to abrupt, clipping a doorlock while running, the brake dragging and heating the brake drum, and the motor field not adjusted properly. Also can be caused by bad boards and loose connections. Good Luck.
