AD7656A return only two values

Dear community,

I have problems with AD7656A. It is connected in hardware mode, with internal reference, VDD/Vss +/-6V, input +/-5.0V max., input channels V1-V6, no STANDBY, CONVSTA+CONVSTB+CONSTSTC tight together, SPI interface, no daisy chaining.

My problem is that it return only two different values when I apply a voltage on input channels :

- -32768d if input voltage is under 0V (every bits low on DOUTA)

- +32767d if input voltage is more than 0V (every bits at 1 on DOUTA)

Same result with all channels.

Ok, my board is not very clean (build on a lqfp to dip board adapter), decoupling is not very good... I suppose it could affect precision, noise, but it's probably not the root of problem. Do you have an idea ?

Thanks for your help,