We use two 7470s to control six fans. Recently we had a fan stall because a third party engineer servicing other equipment stuck a screwdriver through the fan cover. The fan blades were damaged and the fan jammed, fortunately on the broken blade.
When we removed the fan and replaced it the new fan did not start.
Power cycling the box, which is a last resort, restored normal operation.
We can easily detect a stalled fan, the tacho reading goes to 0xFFFF. But then what? How do we get it to run again.
The status bits in ISR2 are clear. The PWM settings are all 0xFE. The other five fans all report normal speeds.
The documentation I have says that a stalled condition is detected and how it can be read, but it does not state that the fan is powered off or how to power it back on again. This feels like it should be very simple, if I just knew how.