Hi, I'm Pete. Welcome to JustAnswer! I'm reviewing your question now, and will post back with your reply ASAP.
Approximately how old is the Speedlight?
What method are you using to set it?
1. Press and hold zoom for about 3 seconds to get into setting mode. 2. Rotate the wheel clockwise two notches to select SLAVE (flashing) 3. Don't forget to press the Set button.
Let me know if that works?
Sorry for the delay, I was offline for a while. Are you looking for details of a repair facility?
To remedy the problem yourself will require specialist equipment and training. Have you worked on or repaired Speedlights previously?
Ok, let me know if you need anything else at all.