I've managed to pass CAL02 like a sharm! Yesterday I've replaced U2420 and had no time to continue. Today I've checked the alignment following Chuck's recommendation. The scope was aligned. But when I went and checked the DAC settings, I could see that they are well calibrated for the whole swing of 2.500V, but now on top they are CENTERED! Perfectly centered. From -1.2501V to +1.2500V!! And before the 1st and after 11th vertical line there is a very little space where I can slide the time marker.
On the calibration signal side, TEK is 1MOhm (not 50 Ohm) terminated and what is required and displayed on the sceen must be output as the HIGH level of the square wave. Zero must be set as the low level of the square wave.
So, the problem was in the marginal performance of the TL084 quad opamp!
Tomorrow I'll try running CAL03, but IMHO it will go w/o any problem,
Thank you very much for all the support and help!