Cooler Master V Semi Modular V550S: revised and better than before!

Input filtering

There are some minor changes in the first stage of input filtration in the Cooler Master V Semi Modular V550S – the film X capacitor and powdered iron core on cables leading to main board are not sleeved with heatshrink. Two ceramic Y caps were not sleeved even before. A resistor has been added for discharging for safety purpose because when the switch is off, the X cap otherwise would not be discharged.


However, the Champion Micro CM02X discharge IC on the board is placed in front of the fuse so it can discharge the capacitor no matter what happens to the fuse. The only scenario when the resistor is useful is when you turn the AC switch off and then unplug cable and touch the pins. Otherwise it is just wasting power, they should have placed the IC directly on the capacitor and saved the resistor, as Sirtec does in their golden power supplies.


There are two more X caps on the main board so the IC may still have some use though. Also two more Y, two common-mode chokes and one varistor (MOV), without any sleeving. So once again same configuration. Thermistor is placed more to the left, after input bridge rectifier and has no heatshrink sleeving too.

X capacitors (between phase and neutral) and Y (between phase and ground/neutral and ground, often also between one side of the high-voltage DC and ground) are used to filter out high-frequency ripple from power grid (often from devices which lack filtration because of cost cutting, but also from devices where filtration is very difficult to implement) and also keeps ripple from this unit from entering the grid. Chokes are used for the same reason, together they form an input filter. These components may also (partially) help to filter smaller voltages spikes in the power grid while the MOV is used to suppress more serious spikes (for example from lightning hitting the power grid at a distance). These days, more Y capacitors are used even between rectified ground (ground after an input rectifier) and earth ground to suppress internal interference and keep it from getting to secondary side, because really high-frequency ripple goes everywhere it can to some extent (including coupling through the insulation, metal casing etc.). That is also why the AC wires themselves are often inserted through the ferrite core.

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