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Reduced resistance of resistor

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leftek:
Hello, from one old board a have put out the resistor 56R 9W, that measured with DMM   1ohm.
Can be one resistor have reduced resistance as fault?

floobydust:
Wirewound power resistors are infallible, and cannot go lower value.
Thick film  (i.e. TO-220) power resistors do go lower value if subjected to small overloads.

The part you have might be something else, like 0.56R 9W or a fuse ?

engrguy42:
FWIW, here's a very brief paper from the US Navy Sea Systems Command talking about resistor failure modes. They claim that around 9% of wirewounds can fail in short circuit mode, and 26% with "parameter change". Which I assume includes a turn-to-turn or other issue causing lowered resistance?

https://www.navsea.navy.mil/Portals/103/Documents/NSWC_Crane/SD-18/ResistorsFailure.pdf

floobydust:
Just bizarre and a crappy report - I can only see wirewound plastic resistors deforming leaving shorted turns, but NEVER for porcelain parts. The report doesn't give any details on construction or methods.

engrguy42:

--- Quote from: floobydust on April 11, 2020, 08:27:59 pm ---Just bizarre and a crappy report - I can only see wirewound plastic resistors deforming leaving shorted turns, but NEVER for porcelain parts. The report doesn't give any details on construction or methods.

--- End quote ---

And neither do you...  :D

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