No wiring diagram or schematic = problem is in our imagination . Sounds simple enough, but if we can't eliminate possibilities, then you'll have to figure it out alone.
Hi,Please post a schematic of you PCB, including the PCB pattern.Have you put a fuse on each PCB?If you are "frying" PCB tracks then you need to provide protection.Did you prototype the circuit before designing the PCB.What on your PCBs has "fried", this will give some indication of the fault.What is the rating of your 12V power supply and what is the load that the 595 are driving.?Remember you are in "troubleshooting" mode, you need to take logical steps to analyse your problem, check each "fried" PCB and look at what has occured.PLEASE put a fuse in your ciruit?Do you have bypass capacitors fitted to each IC?Have you provided the NECESSARY capacitors around the LM7805.Can you please tell us your electronics, programming, Arduino, hardware experience?Tom....
Sure, you could have a blown capacitor that failed short and is allowing excess current draw.You might also try beefing up your 5V rail with another wire in parallel to the trace to eliminate the voltage drop along the power chain.How much current are you sinking/sourcing the the HC595 outputs? Not more than 8 mA per output?
Also, how clean is the DC voltage going into the 7805? If it has a lot of ripple that ripple could be making it thru to the output, and not all caps will be happy with that.