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Re: Cracked resistor?

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Cursitor Doom

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Oct 4, 2016, 6:08:33 PM10/4/16
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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)

Tim Wescott

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Oct 4, 2016, 7:02:45 PM10/4/16
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Yes. But making that mistake isn't beyond me, by any means. It's a very
well-assembled board (I didn't do it), but well designed, too (I did it
-- and I'm modest, just ask me).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

Robert Baer

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Oct 5, 2016, 1:46:18 AM10/5/16
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Plenty of water and the whiskey bottle has been properly drained.

Look165

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Oct 5, 2016, 12:13:52 PM10/5/16
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The dissipation power is 200mW max.

So I lower than 0.3A.

If not, it burns !

Robert Baer a écrit :

J.B. Wood

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Oct 6, 2016, 6:34:08 AM10/6/16
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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,

--
J. B. Wood e-mail: arl_1...@hotmail.com

Michael A. Terrell

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Nov 2, 2016, 2:17:27 PM11/2/16
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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 piss off an Engineer!

They don't get mad.

They don't get even.

They go for over unity! ;-)

Winfield Hill

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Nov 2, 2016, 9:42:00 PM11/2/16
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Look165 wrote...
>
> The dissipation power is 200mW max.

Not much safety margin for an 0603.


--
Thanks,
- Win

tom

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Nov 2, 2016, 11:34:59 PM11/2/16
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"Winfield Hill" <hi...@rowland.harvard.edu> wrote in message
news:nve4k...@drn.newsguy.com...
Isn't that at 25 °C?



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