I'm trying to repair a small electronic door bell.
I was wondering what is the name and purpose of the white box component ?
It seems to be just a wire with some white body around.
Is it a resistor or a fuse? My guess is that 4W22R means 4 watts 22 ohms but I'm not sure.
How can I test that component is still working ?
AFAIK the ground (the black wire) goes through the 400V capacitor first, then it has to go through that white component before going to the bridge rectifier.
EDIT : I found out the issue : the zener diode is dead and acts like a wire (it's always closed). Because of this, the main 400V capacitor is never charging and don't provide power to the rest of the circuit.
I disoldered the diode and tried to put 5.0V directly between the solder joints using a external power supply, it works again !
Thanks Marko Buršič for pointing out the zener diode.
Best Answer
It's a resistor, perhaps wirewound.
Look at the PCB where that component is soldered. Its component designator will probably be a number prefixed by "R". In combination with that capacitor
C25, this is a "capacitive dropper" from the incoming mains voltage.You can read more about that type of power supply in this previous question and elsewhere.
Yes.
With power completely removed and the capacitors on the PCB discharged, you could try measuring its resistance with a DMM and see if you get a sensible result. Since I expect it to be in series with
C25and no other components in parallel with it, then you should measure 22 ohms +/-10%5%The lack of discolouring gives us no indication of overheating (although doesn't disprove that it has occurred).