CPU ventilator check

Some of hefastest PCs around these days, particularly 60-MHz+Pentium and 486- based machines, have a small ventilator fitted on the CPU to help it stay cool. These ventilators are also available as add-on units for PCs which suffer from CPU overheating problems. The circuit shown indicates whether the CPU ventilator is actually running. In fact, the circuit is capable of detecting two fault conditions: (1) ventilator not running because of a wiring fault or a burnt motor winding (i.e., current interruption): or (2) ventilator not running because it is jammed.