The problem is not the design or something else. Please read my post. 12V power supply rail fried and problem occured after that moment. What might be the problem ? I have decoupling capacitors and 1 voltage regulator. I think problem is not the voltage regulator (+-%1 differs every shift register.) For example shift register 1's Vcc is 5.1 V and the second is 5.05 and the other 4.98 and so on. The reason that I dont think the problem is voltage regulator is that the system worked fine until failure of power rails of 3 pcb. I am asking you this, can capacitor failure cumulatively effect the output of the shift register ? Shift register outputs fails after 8th. no matter what the shift register order.