Hello Fratello,

Sounds like a hardware issue. I worked with LM2931 and i had some strange problems because I used a lower capacitance on output. Connect a 100uF (0,1uF is too low) near the stab pack on output line. "On work table" all are ok because may be you use a power supply who have a big capacitance. Also, when pic works with signals its necessary to decoupling with 10uF capacitance.