Check the following points:

• Both devices must have the same frequency channel.
• The transmitter and the unit must be set in the same Sync mode (Normal or Speed Mode).
• Change the frequency channel on the flash unit and the transmitter and test again.
• Is the battery of the Transmitter discharged?
• Are the sync cables working properly?
• Are the camera settings correct?
• Is the unit used in bright ambient light, sun, or halogen lamp directed on the photocell (the photocell may block the synchro circuit on these classical units)?
• Re-check the triggering in a darker room with a minimum of ambient light.
• Check the Transmitter with another flash unit.
• Avoid metal objects or walls between the flash units and the transmitter.
• In case a flash tube is faulty, you can hear the click sound of the flash unit but no flash; this would indicate replacing the flash tube.