The Gi is controlled by a Triac mounted to the power supply chassis. The triac is controlled by a flasher board on the playfiled. This sort of problem is typically caused by a combination of the following:
A problem with the load lamp mounted near the flasher board. Look for a light bulb mounted near the board that doesn't appear to do anything. Make sure it is not missing or has been replaced by an LED
Loose wire or pin connection on the lamp flasher board
Loose connection to the triac,