What safety precaution should be taken before servicing a high voltage capacitor?

Before servicing a high voltage capacitor, confirming that it is fully discharged using an insulated tool is critical for safety. High voltage capacitors can store significant electric charge, which poses a serious risk of electric shock if not properly discharged before handling. An insulated tool allows you to safely check the voltage levels without conducting electricity through your body. By ensuring the capacitor is fully discharged, you mitigate the risk of accidental discharge while working on or near the capacitor.

The other options do not provide adequate safety measures. For example, ensuring it has a residual charge does not address the immediate safety concern of that stored voltage, while checking for visible damage is essential for overall safety and performance but does not directly prevent electrical hazards during servicing. Leaving the capacitor connected is particularly dangerous as it can result in an electric shock, which is why disconnecting and properly discharging is emphasized as the safest practice.