Firstly, check your code against the "Pseudo-Code for Looping AD7731 Through Three Fully-Differential Channels", on page 36 of the AD7731 datasheet rev A.
Confirm the mode register is programmed correctly by reading the register…
Well, I received my SOIC to PDIP socket today and tested a SOIC AD7731 I had and it works as expected.
So, either there is a problem with the PCB I created that shorted out or over volted the DIP parts, or, I received 2 bad DIP parts...
Thanks for all…
I have moved this to the Precision ADCs community, someone here will respond to your query shortly.