First unscrew the two screws at the bottom rear of the controller, slide the case from the front towards the rear. When you look inside facing the front of the controller you will see the bulb on the left it is a bayonet style bulb holder, replace the bulb and reassemble the case.
Also note when the bulb fails it also shuts off the workings of the controller, if there is any other information you require send me an email
vk2acm@gmail.com 73 for now...Clint