This is a repair of two damaged items combined into one. The head showed signs of impact from a fall, so the entire head was replaced. The battery compartment was corroded, so it was replaced. Some external parts were also replaced, including the infrared sensor. When using eneloop batteries and firing the flash at its fastest setting, it goes into "busy" mode after about 20 flashes. Test flashes were easily done 30 times. It goes into "busy" mode around 50 flashes. Infrared slave firing has been confirmed. It fires even when the infrared sensor is pointed in the wrong direction, so the sensitivity seems fine. Please understand that this is an amateur repair before purchasing.