Radio master relay misbehaving

[toto]

Hi all -

My radio master switch has started acting up.  When I turn on the master, power is immediately supplied to the radios while the radio master is off - this is consistent with the expected "fail closed" master relay behavior.  I encountered this on a recent flight - on initial engine start, I thought it was acting a little strange, but chalked it up to flipping the radio master on sooner than I had planned.  On engine start for the return flight, the radio master actually worked correctly and the flight was uneventful.  But on shutdown back home, flipping off the radio master did nothing at all and the radios went off only with the master.

My avionics shop says that it's really strange for a radio master relay problem to be intermittent -- they said that if it fails, it fails, and that the units are normally sealed and unlikely to collect dirt or other gunk that might impact movement.  The plane hasn't made it into the shop yet (just spoke to them over the phone).  I dug around under the panel and found a relay P/N 6041H202, which may or may not be the radio master (I don't really know what I'm looking for).

Is the intermittent relay a symptom of some other problem?  Or do relays sometimes do this?  It's nice that the relay fails closed, but I don't trust it until there's a more definitive answer.  Hoping to get it in to the shop tomorrow, but would love to hear from others who have experienced similar behavior.

TIA for any advice.

[bradp]

Look at this thread.

They are not sealed units and do collect dirt and grime.

I had one of the arms which should be fixed in its plastic frame and makes the electrical contact in the not energized state ("Radio ON") start to wiggle loose over the years probably from vibration.  It didn't fail in the expected way. 

It's not that hard to look at the switch and decide what's wrong and whether to repair or replace (with your AP/IA of course).