Many times we have clients that call us with computers that are unable to start Windows, or stop at a black screen. They try repeatedly to shutdown and startup the computer and then bring it to us for service. As if we sprinkled magic pixie dust, the computers spring back to life and work properly again. While this could all be explained by wizards, pixie dust and co-incidences, the technical truth is that capacitors inside the computer stay charged and keep the computer on, long after it has shutdown.
In fact, not only do the capacitors inside the computer power supply hold a charge, the power supply also provides a low current of power even when the computer is off and all of the fans aren’t spinning. Many computer motherboards have a small green light on the motherboard next to the RAM memory, indicating that the memory is energized when lit. This light serves as a reminder and a warning that there is electrical energy present that could damage a component.
This residual energy can be removed by discharging the capacitors in the power supply and motherboard. This simply involves turning off the power switch on the rear of the computer, and then pressing the front power switch to release the stored energy. If the computer doesn’t have a rear power switch on the power supply, then the power cord will need to be removed. Once the switch is pressed, the fans will briefly spin and the lights inside will go off. Only then is it safe to unplug or insert components inside the computer.
This power off method also duplicates the process of disconnecting a computer and driving it to our office, since the time spent disconnected will allow the capacitors to discharge slowly, allowing the computer to magically work again when it is re-connected.
This power-off procedure is also necessary when a computer is stuck in low power standby mode. When a computer is stuck in standby mode, it will display a power light but the monitor will stay dark. Disconnecting the power and pressing the power switch will force the computer to end standby mode and return to normal power-on operation.