O.K., O.K., I know this issue has been beaten to death previously. However, I have a potentially new bit of information:
N508JS suffered its FIRST flap relay failure today. Flaps were stuck in the UP position and the flap actuator motor was continually running. Pulled the back seat, pulled out the flap relays, replaced them with the spares. Everything works fine now. Total time for the repair = 30 min. No sweat. Popped the covers off the removed relays and sure enough, the contactor was welded to the normally open contact on the relay that occupies socket# 643. Just like almost everyone else has experienced.
Here’s the interesting bit: The relay that went bad was the ORIGINAL FACTORY-INSTALLED relay. Total time in service = 300.8 hours. And, it was a SIEMENS brand relay, not TYCO or the other brand. Also, I inspected the contacts under a microscope when I got home. Lots of evidence of long-term erosion of the contacts (multiple, multi-layered pitting, ionization metal deposits on the non-conductive relay supports and inside cover, etc. Plus, the normally open contact was almost completely worn away; maybe 20% of the original contact surface remained above the metal strip it was riveted to.). Obviously, with less surface area to disperse it, the current finally managed to heat up the contact enough for welding to occur. Perhaps these relays need to have a service life assigned to them and begin being replaced on a regular service interval basis. Any thoughts?