J.B. Wood wrote:
On 10/04/2016 06:08 PM, Cursitor Doom wrote:
On Tue, 04 Oct 2016 16:54:42 -0500, Tim Wescott wrote:

So, a customer sent me a board with the query "whuzzup?"

It turns out that there's a resistor in there, which I mostly put in so
that I could monitor current, but I kinda put in as a last-ditch fuse
(1.5 ohm 0603).

On this board, the resistor is open-circuit with no discernible burning.
Is there some electronic mechanism that could cause this? Or am I just
looking at a faulty part?

I assume you've got your test prods directly on the pads so you know it's
not just a dry joint?

X-posted to s.e.r (more appropriate group)


Hello, and the only similar problem I've encountered is with those
sandy-colored dropping resistors (rectangular parallelepiped shaped)
that have been used in radios and TVs. They can swell and/or crack over
a period of time. Repeated heating and cooling no doubt stresses the
resistor material. Sincerely,


Some of those are 'Fuse Resistors', and are designed to fail open if
the equipment starts drawing too much current, or if it is running too
hot. I replaced hundreds, if not thousands of those in consumer
electronics. Some OEMs switched to the Belfuse 'Chemical Fuses', which
had a chemically coated element that would flash and vaporize the
element at a set temperature.

They were quite common, in spite of Phil Allison's claim to the
contrary.



--
Never **** off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)