Fixing a fart-extractor (with schematic)

Описание: An inline toilet fan with timer that was sent in by Will (physicmad).

In the UK we use toilet/bathroom fans that have a continuous and switched feed. When you turn on the light in the room the fan starts, and then continues to run for a fixed time after the light has been turned off again to purge any aromas or excessive humidity.

The circuitry is usually very minimalist, using a current limiting resistor that is sometimes prone to cooking to the point that it can sometimes short out in some brands, with undesirable results.
It's been pointed out that the resistor may double up as an anti-condensation heater to keep the enclosure dry.

This unit has an intact resistor, but Will said the timing started getting shorter and shorter and the fan would sometimes struggle to start, even though it was free to spin.

Can you guess what the fault was?

The easiest fix for some of these is to remove the PCB and add a bit of terminal strip to run the fan off the switched feed. Just remember to leave the light on for a while after a bath or shower to remove the humid air.

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