What precautions should I take before opening the control box?

Before inspecting the inside of the control box, turn off the power and leave the unit turned off for at least 10 minutes. Check that the voltage of the electrolytic capacitor (inverter main circuit) has dropped to 20 VDC or less, as the unit may remain energized or hot after power is turned off. It will take approximately 10 minutes for the voltage to discharge after power off. (Page 15)