The overcurrent LED can blink if an arc or HV breakdown occurs in the coax cable or load. This is more likely if the cable is old, if you're using a cable not supplied by us, or if you are running more than the specified absolute maximum of 10 kV.
An overcurrent condition can also occur (and trigger the overload circuit) if the load capacitance is too high, such as from using an excessively long cable.
If the Overcurrent LED illuminates, the pulse output will be inhibited for 6-7 milliseconds. Also, the overvoltage protection circuit may conduct if the output exceeds 10 kV. Either action will affect the output waveform.