Cracked resistor?
 

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)

Cracked resistor?
 

On Tue, 04 Oct 2016 22:08:17 +0000, 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)

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!

Cracked resistor?
 

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)
Plenty of water and the whiskey bottle has been properly drained.

Cracked resistor?
 

The dissipation power is 200mW max.

So I lower than 0.3A.

If not, it burns !

Robert Baer a écrit :
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)
Plenty of water and the whiskey bottle has been properly drained.

Cracked resistor?
 

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,

--
J. B. Wood e-mail:

Cracked resistor?
 

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! ;-)

Cracked resistor?
 

Look165 wrote...

The dissipation power is 200mW max.

Not much safety margin for an 0603.


--
Thanks,
- Win

Cracked resistor?
 

"Winfield Hill" wrote in message
...
Look165 wrote...

The dissipation power is 200mW max.

Not much safety margin for an 0603.


--
Thanks,
- Win

Isn't that at 25 °C?