The first thing to make sure any plug-in ICs are siting properly in their sockets. If any have been removed, remove them again and check that their pins are straight, often if they are not put in properly, the pins bend through 120 degrees underneath the chip and the only contact is with the "knee" of the pin just touching the IC socket,which will loose contact over time with oxide/vibration. Else look for smoke, over heating resistors or chips, bubbling capacitors.
What should an "ARC" unit do? What do your ones do?
Frank