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How can I find out the value of this burnt-out resistor from a power supply?

burnt-out resistor

I've tried a few online resistor calculators and every single of them gives different values ranging from 0.1 ohms to one gigaohm. I've tried substituting gray for silver, reading the bands from both directions and leaving out the last band. My multimeter gives readings over 2 MOhms.

Edit: The resistor was on the hot primary side of the power supply, residing between the transformer and some SMDs on an otherwise through-hole design. A 0.1 ohm shunt resistor for current sensing is a likely candidate. Looks like many if not most online resistor calculators freak out when they see a gold or silver band where they would expect a normal color.

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  • \$\begingroup\$ I wouldn't trust what the DMM says, even as a ballpark. \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Feb 1, 2014 at 12:54
  • \$\begingroup\$ I would read it as either brown-black-silver-gold (0.1 ohm, 5%) or possibly red-black-silver-gold (0.2 ohm, 5%). Probably a current-sensing resistor of some sort. Can you reverse-engineer the board it came out of at all to get an idea of how it was used? \$\endgroup\$
    – Dave Tweed
    Feb 1, 2014 at 13:12
  • \$\begingroup\$ The bad news is that this resistor was connected to something that didn't turn off because it's fried, most likely. \$\endgroup\$
    – Spehro Pefhany
    Feb 1, 2014 at 13:18
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    \$\begingroup\$ Speculation: The silver and gold bands indicate a fractional Ohm value, so it was possibly a current sensing shunt resistor. Since we are all lazy, current shunts are most often selected as 0.01, 0.1, 1 etc, to make the calculation simple. Thus, my contention is that this was a 0.1 Ohm resistor. \$\endgroup\$
    – Anindo Ghosh
    Feb 1, 2014 at 13:20

1 Answer 1

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Looks like brown black silver gold black.

According to this web page, if the fourth band is gold or silver, the 5th band is temperature coefficient.

That makes this 0.1 ohm, 5%, 250 ppm/degree K, which makes perfect sense for something like an overcurrent sense shunt.

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