Electronics > Repair

Bathroom timer fan repair faulty Vent-axia VASF100T pulses or runs slow

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rh100605:
I have two of these that have suffered the same fault so it must be very common. The fan slows down or starts only sometimes or even pulses.

The circuit uses ten 8.2K 1206 smd resistors  in series/parallel to form a 20K 2.5w resistor to drop the 230V live to a 3v3 zener with a 220uf 10v electrolytic capacitor across it.
This forms the 3.3 volt supply for a Sonix microcontroller that is clocked by the line input and drives a 1amp triac in series with the motor.

As the capacitor (EC1 next to the corner fixing screw hole) is live all the time and kept warm by the dropper resistors  it eventually fails. The 3V3 supply then develops significant pulsing.
When triggered by the switched live, the SN8P2501D 8-Bit Micro-Controller keeps thinking that 3.3 volt DC power has been lost and restored.

Replacing the electrolytic with a 105 deg C, FR range 220uf 16V from Panasonic restored working.
I have a suspicion that many other makes of fan with a run on timer will suffer  a similar fate.

There is even a video on You Tube "Trying to FIX a Bathroom Extractor Fan that doesn't run on" which swaps out a 330 uF 16Volt electrolytic  kept warm by a large 22K wire-wound resistor!
Happy fixing

ringzer:
You mentioned that the existing capacitor was 220uf 10V but you replaced it with 220uf 16V. Is that correct? And if so, why did you do that?

Thanks

Gyro:
16V electrolytics tend to be more common than 10V ones, certainly in peoples' parts bins. There is no issue with replacing an electrolytic capacitor with a higher voltage rated one, as long as the package will still physically fit. Doing this can even improve reliability if the manufacturer has 'cheaped out' and hasn't left enough margin between the capacitor rating and the voltage it is actually experiencing (doesn't appear to be the case in this example).

ringzer:
Ok, thanks for the prompt reply. I'll take apart the fan and see what's inside before ordering a replacement. But good to know 16V would work just as well

floobydust:
The electronics is powered up 24/7 and the parts don't last so long.
The 220uF 10V electrolytic fails and the dropper-capacitor can also. This is the grey boxed one at the end? Test them both for low value.
edit: it was the grey capacitor on another Vent-Axia, but this model has three other film caps which I think are for the fan motor.
I don't think resistive-dropper has enough power for the triac but maybe.

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