Reply to Calbration problem technics 1210

So I already calibrated some turntables, but this one still don't want to be calibrated

The problem is:
-I had 2 zero positions
-Putted it on the second zero position
-Measured the value with a multimeter
-Putted the pitch back in the middle
-Turned the potentiometer on the same value as with zero-position 2

---> Now instead of having 1 zero-position, I have a zero area (from 0% to +1%)
The remaining area of the pitch function acts perfectly normal.

Anyone knows how this problem can be solved?

Thanks!