AOUT_LC calibration MBSEQ4

[Schrabikus]

This is my fourth or fifth unsucsessful attempt for last half-year to calibrate AOUT_LC module.

Yesterday i've replaced R49/51 with 100k ones and get perfect calibration for 1V, 2V and 4V values. But i have 11,22 instead of 8V. Or 0/11,22/11,22 with Min/Mid/Max

Replaced opamps, shift registers, checked all resistors and here what i have.

(1 - Vdd 4,95v)

I was confused by one point - why there's non linear value of 4,32v at 8V calibration setting. Is it R-2R related? I measured resistance between shift register outs and opamp inputs. Is it looks acceptably?

Shift register? I replaced it three times with different suppliers ones.

Or maybe it's software related?

I'm totally confused and need your help.

PS. Bipolar supply values is +11,87/-11,97

Edited May 8, 2012 by Schrabikus