At 03:08 AM 2/11/2013, neil n wrote:
>again. I saw 560 Ohms but then saw ~ 60 Ohms. What? Figuring the DMM
>probes were dirty (why would they be?), I cleaned them.

Not relevant to this instance, but in fact the plating on meter
probes is somewhat notorious for giving difficult contact under some
conditions.  Any kind of intermittent reading when using hand-applied
probes should lead to suspicion of that contact.

Best probes I ever had for general-purpose use had collet chucks at
the ends with inserted hardened steel phonograph needles or the
equivalent.  Would penetrate most anything, wouldn't slip.

>  Most readings
>were 560 Ohms but then a few were 60 Ohms so I had a closer look at
>the relay terminals. One felt slightly loose.
>
>Can you see it? Image:

Well that's very interesting.  Seems to be a fatigue fracture of the
wire itself.  I'm guessing it was induced by vibration coupled into
the terminal.  Notice it happened just at the stress raiser point
where the wire enters the massive joint.

Yours,
David
ps - Neil, you should get hold of a Stereozoom scope or similar and
turn up an eyepiece adapter for your camera for it.  The little
pocket cameras are ideal for this because of their very small sensors
which allow the narrow beam of light from the eyepiece to fill the
camera field without much zooming.  But with or without the camera
you'll be amazed at what you can see with the scope.  Typical zoom
range is 7-35 diameters, and working distance about four inches.  I
made an industrial-type overhanging mount for mine from bits and
pieces of a couple drill press adapters.