I've just bought a Yongnuo RF-600TX transmitter but it looks like it doesn't work with my YN-560 IV flash. Does anyone know how to set up these things?
The RF-600TX is a Yongnuo RF-602 transmitter (just without the PC input port on top).
The YN-560 IV defaults to using the RF-603 communication protocol, which is different. You have to set it to use the 602 communication protocol if you want to remotely fire your flash from an RF-600TX transmitter.
The manual says that this is an "Advanced Options Setting". To access it:
Press the [Illumination/Sound] and [MODE] buttons at the same time to enter the menu for setting the options.
Press the [UP] or [DOWN] buttons until you are on the rF setting.
Press the [RIGHT] or [LEFT] button to change the setting from 60 3 to 60 2.
There aren't instructions in the manual for getting out of the menu, but I'd assume hitting the [SET] button in the middle of the four-way buttons would do it.
After you've done that, so long as the flash is in radio slave mode and set to use the same channel as your RF-600TX, they should communicate with each other.