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Home hobbyist here. I'm trying to be a little more automated in my reading of resistors. I've gotten pretty good at reading the 4 bands with the beige background, I find the colors easy to read, and the tolerance band obvious (gold or silver).

But these blue resistors drive me nuts. Honestly, I could read this in both directions. Is this just a case of cheapo manufacturing and the need to manually measure it, or am I missing something?

enter image description here

BTW, this measures to 10 kΩ, but to me, the tolerance band looks to be the same color as the brown first band, and could easily be read (from right to left as pictured) as "brown-red-black-black", or 120 Ω.

Is there some trick I don't know about?

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3 Answers 3

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It's just bad markings. The bands are supposed to be shifted in position so there's a larger gap between the multiplier and tolerance bands than the first and second digit bands.

Those bands are horribly misshapen (looks like a toddler painted them on) and your guess would be as good as mine. The only vague indication that the right hand band might be the tolerance band is that it's very slightly thinner, but honestly there's every chance that if you picked out another resistor from the same batch it'd be just as thick as the other bands.

In cases like this you just have to measure the resistance.

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It's a 10kΩ 1% resistor. 120 is not a standard E96 series value so 120Ω 1% is unlikely, but not impossible.

Since it is a standard E24 value though, as @Hearth correctly points out, many makers have upgraded their 5% resistors to 1% tolerance and offer 1% resistors in the E24 series, so that's not a 'tell'. Measurement is the only way to be sure. Still better than smaller SMT parts which are not marked at all.

Typically the bands are more offset than that.

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    \$\begingroup\$ Note that 120 Ω is a standard E12 and E24 value, so it's not that unlikely. Nominally, E24 is for 5% tolerance, not 1%, but you can get E24 resistors in 1% tolerance; 120 Ω ±1% appears to be a standard product in lines from Yageo, several divisions of Vishay, TE Connectivity, and Stackpole, just looking through Digikey. \$\endgroup\$
    – Hearth
    Commented Jan 17, 2023 at 3:22
  • \$\begingroup\$ @Hearth excellent point! \$\endgroup\$ Commented Jan 17, 2023 at 15:00
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The resistor is 10K, tolerance 1% (E96 series), where 1st, 2nd and 3rd bands are significant digits (100) and the 4th band is the multiplier (10^2=100), resulting in 10000 ohms = 10K. The 5th band (brown) represents the 1% tolerance. The resistor cannot be read backwards because 120 ohms is not commercially available in the E96 series (1%).

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    \$\begingroup\$ Of course they are "commercially available". Here's just the first example I found on digikey: LR1F120R with 50000 in stock. \$\endgroup\$
    – pipe
    Commented Jan 18, 2023 at 6:46
  • \$\begingroup\$ Okay, 120 ohms might be commercially available according to @Spehro Pefhany. But it is not standard on E96 series according to IEC 60063:2015. \$\endgroup\$
    – Luizzz
    Commented Feb 23, 2023 at 16:19
  • \$\begingroup\$ I would also add, as a hobbyist, I'm not innately aware of what is typical or available or not. \$\endgroup\$
    – LarryBud
    Commented Feb 8 at 16:44

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