I have successfully setup a RTC clock ( DS3231 ) on a RPi zero. The whole process was explained here. It works as expected but with only a minor difference: Row 5 is filled with numbers from 0x50 to 0x5f. There are guys here who complain about all cells filled, but in this case only a row is fully filled. What could be wrong here?
UPDATE: I have not removed the pull-up resistor on the DS3231 board. Well, here are the photos that may help.