Improvements of the power supply

Inspection of the power supply of the module reveals that two components are missing: C1 and R4.

These two components are important for security and filtering out noise, but were not mounted by the factory, probably to save money. So, these should be added.

Safety capacitor

The capacitor is usually a polypropylene film capacitor suitable for 275VAC, which adheres to the standard EN60384-14. Its purpose is to filter out interference.

The optimal value for (European) 240VAC mains voltage systems is 100nF. The PCB hole spacing is 10mm.

MOV varistor

The resistor R4 is a metal oxide varistor. The PCB hole spacing is 10mm.

Such a varistor protects against overvoltage transients on the 240VAC mains. The most suitable and safe value should be 10D561.

As a protection against catastrophic MOV failure, the varistor should not be used without a series connected thermal fuse. The board has a SMD serial fuse fitted at the botton side.

The result