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EVAL_AD7984_PMDZ - probe voltage

I got the EVAL_AD9784_PMDZ and Zedboard reading data. It is differential ADC, 2 probes with 1 common ground. The ground is at the ZedBoard GND level (as expected). The voltage input is +7.5, GND, -2.5 V on connector J3 - according to specification and GND, 3.3V from PMOD connection on Zedboard.

Lately, the probes are giving off voltage of 2.5 [V]. I would like to ask, whether it is faulty behaviour.

I havent measured the difference between probe and ground before, when it seemed to work properly, but I would expect the probe wouldnt force any voltage on measured signal.

The measurement:

One probe is connected to GND (all grounds are at the same level) the other is connected to positive input.


P.S. probe = analog inputs on the board