we have 4 designs with basically the identical schematics. 3 are working fine but the ADC in the 4th one returns a 0 or 2041 steady value. We are using the same code on all 4 designs. All connection have been verified and the chips on a working and the non-working design are from the same purchased tray.
The only clue is that the ADCREFM voltage on the non-working design is higher (~1.5V) than the ADCREFP (~1.2V). while the ADCREFM oon the working designs is around (~0.8V).