Slc free 2 not working well

My slc free 2 is not working well, the screen is stuttering and sometimes shows question marks and stange symbols.
I assebled all together and tested it, no proplem, 2nd time i tested it started acting stange and now only show lamba on top and 2 bars (like this | |) on botom, and value is static
Already checked every solder and the cable, still having isues.
What should i do?

check the soldering on the 16 pin LCD connector on both boards, clean the contacts with rubbing alcohol.