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I need to replace a resistor (brown black black gold black - if I am reading it correctly) - the kind I need is shown in the images below, but I can't seem to find an exact match of the colour code. Is the black (5th) line at the end of the code superfluous - so this is in fact just a 4 band code (making it a 10 Ohm 5% resistor)? From my research it appears that a resistor code would almost never start with black. However a 5 colour resistor of similar pattern doesn't appear to often end with black either...

Detail: I am repairing a toaster where one side (2) of the 4 toasting slots have stopped working. Each side operates independently so I am using the working half as a guide to repair the blown side.

Resistor: Brown Black Black Gold Black

Here is the blown resistor from the damaged side of the toaster - I'm working on the assumption that this is carbon film resistor. Blown resistor

Oliver Jobson
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    *"... a resistor code would almost never start with black"*: Example starting with black: *[4/5 band resistor - extra black band](https://electronics.stackexchange.com/questions/171289)* (black - brown - red - silver - brown) – Peter Mortensen Jan 07 '18 at 17:54
  • just fyi: typical tables do not include BLK as a viable option for tolerance. Hence, BLK cannot mean tolerance, so GLD is the tolerance, and the extra BLK means another thing: temperature coefficient (or 250.. pretty bad one, so I doubt it), or non-inductive wire winding (that's a low-R power resistor, so it's quite probable), or something I haven't read about yet. – quetzalcoatl Mar 09 '21 at 13:06

4 Answers4

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It's a 10 ohm 5% resistor. Sometimes a black band, centered over the end cap, is added to make it more obvious which is the right-hand end.

The part appears to be a wirewound type, possibly designed to be fusible. A carbon film replacement might be a safety hazard.

Spehro Pefhany
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  • 'obvious'? aren't the sides already obvious since preceding band is gold, and it cannot be the first band, as gold has no number assigned? from what I read elsewhere, last black band is either TemperatureCoefficient=250PPM, or a special marking "non-inductive" at least for 2w/5w resistors. – quetzalcoatl Mar 09 '21 at 12:56
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    @quetzalcoatl The ones we sourced they put the black band on all the resistors as a matter of course, not dependent on the other colors that happened to be required for the specific values we ordered. This was direct from the factory. – Spehro Pefhany Mar 10 '21 at 01:38
  • Ah, I see, makes sense. From manufacturer's POV, it's definitely simpler to just blindly add an extra band of some predefined color than to analyze when/why/whever it is actually needed. Thanks! – quetzalcoatl Mar 10 '21 at 21:58
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It appears to be a wirewound power resistor, and I believe it's 10 ohms +/- 5% with the 5th band representing the temperature coefficient or reliability.

EM Fields
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This will probably help: -

enter image description here

So, you resistor is 100 x 0.1 ohms = 10 ohms

The black band at the end implies there is no tolerance.

Andy aka
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  • there is no such thing as "no tolerance", except for no tolerance for racism :) jokes aside, "no tolerance" would mean that you bought 150k resistor and it's actually 0.1 ohm and all's fine. In that table, also orange and yellow and white don't have tolerance value defined, a nice hint that's not it. That table simply skipped this case. An old resistor may have no tolerance band, and that means we should consider it to have +/-20%. Last band of black actually may mean temperature coefficient of 250ppm, or as I just read, it may also mean "non-inductive" for low-value high-watt power resistors. – quetzalcoatl Mar 09 '21 at 12:59
  • @quetzalcoatl look at the picture - there is no tolerance quoted in the picture for a black band and many thanks for the ill-placed pedantic downvote. – Andy aka Mar 09 '21 at 13:22
  • Then please do look at other tables, like [here](https://web.ua.es/docivis/magnet/electronic_color_code.html) which hold my idea that this is a 25ppm or [this](https://eepower.com/resistor-guide/resistor-standards-and-codes/resistor-color-code/#) saying the same, or [even here](https://www.researchgate.net/figure/Resistance-color-code-chart-with-examples-of-4-and-5-band-resistors_fig1_325967064) which claims it could be +/-20% and this one is exceptionally interesting, as it comes from 'researchgate' portal and actually includes a very exotic "-0%/+100%" yellow tolerance. – quetzalcoatl Mar 09 '21 at 13:31
  • I dared to drop a -1 because I wanted to draw your attention to the fact, that there never is a "no tolerance" for a component. If it's not specified, it's implicit 20%. And with the abundance of broken or incomplete tables, the fact that "hey, there's nothing here in this cell" doesn't really have to mean that this component has "no tolerance".. and yeah, I see it's a one-shot 5-yeard old thread.. sorry for pendantism, I'm pretty frustrated trying to decode my case – quetzalcoatl Mar 09 '21 at 13:33
  • @quetzalcoatl please stop wasting my time and look at those tables correctly. The tolerance band has no meaning when the band is black. And I downvoted your question because your motive for downvoting me is not reasonable. My downvote of your question was reasonable (if somewhat retaliatory) because you showed a distinct lack of research when making your question. Do you see why you should be careful about making downvotes. – Andy aka Mar 09 '21 at 13:34
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Base on mr. EM Fields answer i think its 10 Ohms, zero tolerance i.e first ring denote one and second denote 0(zero) and three denote another 0(zero) and the last zero too. This will equall 1 & 0 & 0 × 0.1 = 10 and the last ring which is zero(black) So thechnically i think it's 10 ohms 0 tolerance resistorAn example of same kind of ristor on a potable power converter

Nsikak Friday Akpan
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    There's no such thing as a zero-tolerance resistor, though. – Hearth Jul 05 '20 at 14:09
  • 1. Your "resistor" is marked "RF1." I expect it is in fact an inductor to keep noise from the switching power supply from getting back out to the outlet. 2. The capacitor in the lower left corner of the picture looks like it has gone bad. The top is "popped." Electrolytic pop their tops when they get to hot. – JRE Jul 05 '20 at 17:21
  • Yep the capacitor is bad and i did replace it. thanks for the correction on resistor tolerance "There's no such thing as zero-tolerance resistor" as quoted. – Nsikak Friday Akpan Jul 16 '20 at 17:31
  • @JRE "Resistor Fuse" – mow Dec 13 '22 at 23:41