Transient Filtering Stage
As we mentioned on other articles, the first place we look when opening a power supply for a hint about its quality, is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components than that, usually removing the MOV, which is essential for cutting spikes coming from the power grid, and the first coil.
This power supply filtering stage isn’t good at all. It features only one ferrite coil (instead of two) and two Y capacitors. There is a ceramic disc capacitor labeled as “J101” but this capacitor is connected in series with the main AC power line instead of in parallel. So this power supply missed one MOV, one ferrite coil and one X capacitor just to have the basic recommended components for this stage. It is interesting to notice, though, that there is empty space for installing the X capacitor (labeled “CX102”) and the second ferrite coil (labeled “LF103”). So, some models using this same PCB may have a more complete filtering stage (which is the case of Ultra X-Connect 500 W and the model sold in Europe by Levicom) – but still missing the MOV. The European version also features passive PFC.
We found something really bad on the model we disassembled: it hadn’t a NTC thermistor. As you can see in Figure 10, it had, instead, a wire jumper on its place (labeled “TH101”).
In the next page we will have a more detailed discussion about the components used in the Young Year YP-AB.