Canon Speedlite 600EX-RT Instruction Manual page 111

Radio Transmission Wireless Shooting
Wireless shooting does not work.
When using a Speedlite 600EX (without radio transmission function),
wireless shooting using radio transmission is not available. Use optical
transmission wireless shooting.
The slave unit does not fire.
Set the master unit to <'> <M> and set the slave unit to <'>
<x> (p.52).
Set the transmission channels and wireless radio IDs of the master unit
and slave unit to the same numbers (p.52 - 54).
Check that the slave unit is within the transmission range of the master
unit (p.48).
The camera's built-in flash cannot be used as the master unit in radio
transmission wireless shooting.
The slave unit does not fire or unexpectedly fires at full output.
Run the channel scan and set the channel with the best radio reception
signal (p.54).
Position the slave unit in clear view of the master unit, without obstacles
between them.
Face the slave unit's front toward the master unit.
Pictures are overexposed.
When using autoflash shooting with three firing groups A, B and C, do
not fire with firing group C pointed toward the main subject (p.63).
When shooting with a different flash mode setting for each firing group,
do not fire with multiple firing groups set to <a> or </>
pointed toward the main subject (p.67).
Troubleshooting Guide
109