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Resistor failure from cold?

An amplifier stored exposed to our last UK winter , maybe dropped to -15 degrees C. Loss of the negative side of the biasing area of one channel. By a secondary route there was some negative V around , did not rise to + rail or centre and difficult to find as no reason to suspect a small o/c R. In an area with only -15V secondary supply and loads of 1N4148 and TO92 around. This resistor was normal 1/3W

4K7, not a fusible resistor, metal oxide spiral construction. On scraping off the coating , break was 1.5 turns along the 5 turns, ie not central. Absolutely no sign of heating on original R surface or the board and no sign of heating with the coating removed. A closely defined break , probing with DVM. But nothing seen in the way of a crack , bubbling, corrossion or discolour even under x30 magnification. Could not close the break by twisting or bending the body of the R. I've come across mechanically broken R from being dropped but never from cold or damp.
Reply to
N_Cook
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Maybe just age or cheap source of parts. In the past year or so I have had a bad 56 K resistor, a bad 39K resistor, and a bad 18K resistor, all in amplifiers, none burned or stressed. Two of them were in units about 25 years old; the other about 10 years old. Caused by your cold winter? Perhaps, perhaps not. Co-incidence doesn't necessarily mean causation.

Mark Z.

Reply to
Mark Zacharias

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I expected to see a manufacturing void in the MO or something like that, so some thermal stress met the camel's back.

Reply to
N_Cook

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Microscopic nick on the wire may have contributed to the failure due to=20 wire shrinkage from cooling.

Still most parts are designed to handle from at least -40C to +80C in=20 storage. Here is a link for a paper about testing ww resistors from -55=20 to +225C with only one failure:

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"Wirewound resistors were also thermal cycled 1000 times over a=20 temperature range from -55=B0C to 225=B0C with only one failure due to a =

broken internal connection. "

John :-#)#

--=20 (Please post followups or tech enquiries to the newsgroup) John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)

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"Old pinballers never die, they just flip out."

Reply to
John Robertson

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Microscopic nick on the wire may have contributed to the failure due to wire shrinkage from cooling.

Still most parts are designed to handle from at least -40C to +80C in storage. Here is a link for a paper about testing ww resistors from -55 to +225C with only one failure:

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"Wirewound resistors were also thermal cycled 1000 times over a temperature range from -55°C to 225°C with only one failure due to a broken internal connection. "

John :-#)#

-- (Please post followups or tech enquiries to the newsgroup) John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)

formatting link
"Old pinballers never die, they just flip out."

+++++++

This was metal oxide type. Returning to it I realised I was looking on the wrong side of the body under the microscope. The failed section was distributed , puckered and a bit discoloured presumably from condensation/corrossion and parts flaked off , probably came away with my breaking off the coating.

Reply to
N_Cook

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Ah, right, metal OXIDE (do I need better glasses?)...oh well, at least=20 you found the culprit!

John ;-#)#

--=20 (Please post followups or tech enquiries to the newsgroup) John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)

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"Old pinballers never die, they just flip out."

Reply to
John Robertson

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