I am trying to repair a HoMedics foot massager which now only works for less than a minute before switching off.

I think I have identified the cause of the fault as the dropper capacitor (X2 684K). It is measuring around 100nF.

There is an 8 pin SOP on the back of the PCB marked WL508SNJ but I can't find any data on it.

Would any X2 680nF capacitor with 275V or greater rating be suitable as a replacement?

 

Can anyone advise?

 

Is that measurement of 100nF with the capacitor in circuit; often capacitance measurements are off where parallel resistive/semiconductor paths are present.

Whenever I want to avoid this issue I carefully cut one leg (of the capacitor) to make the measurement, then re-solder the cut parts.

By their nature X capacitors are very reliable, I’d be surprised if a genuine X2 capacitor value dropped from 680nF to 100nF.

Of course the change in capacitance value may not be the reason for the fault.

Yes, any X2 capacitor of 680nF having a voltage rating of at least your mains supply voltage will be OK.

 

Can anyone advise?

Hi,
Looked into the circuit.
The 8 pin chip WL308SNJ is a dedicated application processor working off 5V.
Pin out:
1. GND 0V
2. LED Output
3 LED Output
4. spare I/O ( tied lo )
5. Heat control Output
6. Motor control Output
7. Push Button input
8. Supply +5V

It is a custom IC and no spare part available, however they are unlikely being the culprit.

The two high voltage capacitors in the circuit are of poor quality and actually degrade over time.
The 680nF is part of the Transformerless Power Supply (Capacitive Dropper) which would result in irrectic behaviour when its value drops below a value which could not sustain the supply to the circuit especially when the LEDs starts draining power from the circuit.

One tell-tale sign is that the DC voltage between anode of D2 and catchode of D1 which should be significantly higher than 5V can be seen dropping below 5V when button is being pushed.

Replacing the capacitor even with a 470nF 275V X2 rating would get the circuit working again although I would replace it with 680nF for better margin.

I would expect quite a few such failures in the field.