Question: how to pair sony bluetooth headphones mdr-zx780dc?
Answer: Unlock the screen of the iPhone.
Turn on the headset. Press and hold the POWER button for about 2 seconds. Make sure that the indicator (blue) flashes after you release the button. ... 
Search for this headset on the iPhone. Select [Settings]. Touch [Bluetooth]. ... 
Touch [MDR-ZX780DC].