Voltage regulator replacement
U5 looks like it could be your 5V (or 3.3V) switching IC. 
I'd imagine there's 10V coming from the 7818 into U5 from a 12V input. 
You can look up the data sheet from the MCUs and trace the Vcc pin and see what's powering it. Work backwards to find where the problem might be. 

The suffix is usually the input voltage range it can take. Some 78xx can take up to 35V.