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I have a 5W 5-banded resistor that shouldn't exist according to the color code chart and I've never come across this before.

The color bands are brown, green, silver, gold, black. Now looking at it in both directions it's not a part of the logical code. It's definitely not white; it's shiny silver. The gold is definitely not brown as it's different; not orange but a sparkly gold band.

La Resistance

So am I just dumb or crazy or have I got some specifically made junk that im going to have to stack some to get my Ωs?

I get no reading when using a meter, not even M or natta, in circuit or out. They act like 0Ω resistors but obviously they at least used to have a soul.

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  • \$\begingroup\$ what are the associated labels on the board? \$\endgroup\$
    – jsotola
    Commented Nov 17, 2021 at 9:18
  • 1
    \$\begingroup\$ What equipment are they used in, that could give a clue. If it's an audio amp, they could be class AB emitter resistors. Could they be inductors? If they are << 1 ohm, they will be impossible to measure with a DMM on ohms range. Try doing a 4-terminal measurement to get a proper reading, so the voltage drop across them when they conduct 10 mA, or 100 mA, from an external power supply. \$\endgroup\$
    – Neil_UK
    Commented Nov 17, 2021 at 9:38
  • \$\begingroup\$ Clearly it does exist. \$\endgroup\$
    – winny
    Commented Nov 17, 2021 at 10:49
  • \$\begingroup\$ Duplicate : Strange resistor colours \$\endgroup\$
    – J...
    Commented Nov 17, 2021 at 18:52
  • \$\begingroup\$ As a more general answer, gold for multiplier is well-recognized to be 0.1 and and silver is 0.01 which matches @Justme's answer. \$\endgroup\$
    – penguin359
    Commented Nov 17, 2021 at 20:32

2 Answers 2

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Most likely 0.15 ohms, 5% tolerance, and the black might mean something special.

In some sources, it indicates a temperature coefficient of 250 ppm/K.

In other sources, it indicates non-inductive resistor, which is likely here.

In yet other sources, it indicates the resistor reliability or failure rate. Black is not a known color for failure rate so likely it is not this.

Finally, some manufacturers like to indicate a fusible resistor with a manufacturer specific color.

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    \$\begingroup\$ +1 And Related : the black band just indicates the reading direction (read towards the black band). Seems this was one of those transient standards that didn't stick around. \$\endgroup\$
    – J...
    Commented Nov 17, 2021 at 18:51
  • \$\begingroup\$ From what I see elsewhere, I think failure rate normally replaces the tolerance band instead of being the last so I would go for the black band being either temperature coefficient or a marker for reading order. \$\endgroup\$
    – penguin359
    Commented Nov 17, 2021 at 20:30
  • \$\begingroup\$ @penguin359 I'd say it means non-inductive. It's only a 5% resistor so it's a bit imprecise for having a rated tempco. But if that is an audio amplifier, and the resistors are the bias resistors, both non-inductive and stable tempco would make sense. \$\endgroup\$
    – Justme
    Commented Nov 17, 2021 at 22:02
  • \$\begingroup\$ @penguin359 Definitely reading order. Temperature coefficients don't show up until you reach six band precision - otherwise the tempco just lumps into the standard tolerance. \$\endgroup\$
    – J...
    Commented Nov 17, 2021 at 22:11
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These are most likely fusible resistors, which combine current limiting (resistor) and failsafe overload behavior (fusing).

There are a variety of color coding used to indicate this ("Colour codes for fusible or non-flammable resistors"), with a white last ring being most common, but green and black last ring also being fairly common.

Replacement should be with other fusible resistors to maintain protection. As with fuses, you will need to locate and repair the cause of the overload, otherwise the fusible resistors will just fail again.

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