Resistor Reading – Which Way to Read This Five Band Resistor?

resistors

Sorry for this basic question. I have a problem determining which way I should read band on the resistor below. I know it's left to right, but which side of it really is "left"? As far as I know, this board was assembled manually, so the orientation of the resistor on the PCB is basically random, or at best unreliable.

  1. On one hand, it seems gold should not appear on the second place, so I should read it the way it appears below, as brown black green gold green.

  2. On the other hand, usually the first band is the one closest to the end of the resistor, and that would give me green yellow(?) green black brown.

Difference between 10.5Ω and 545Ω is quite big, so I need to figure it out.

And yes, I tried to measure it. Currently it's 0.98 MΩ. Give or take some as I'm using cheap multimeter for the lack of a good one. I believe it's burnt, that's why I'm in need of a replacement.

I asked my friends first and they still argue, so I figured out it's time to ask for an expert help. I also asked the manufacturer, but don't know when and if he'll reply.

resistor photo

Best Answer

If you measured 1 Mohm it is about right. It's a 1 Mohm 5% special resistor. It is not clear why you think it is burned, as it looks just fine and measures accordingly, so there is no reason to believe it is burnt and there should be no reason to replace it.

So to know how to even begin decoding the colour codes, it must be understood that there are different ways of encoding them, so even if there are five colour bands, it does not mean that a generic five band colour scheme can be used, as there are exceptions like in this case.

So first of all is to determine which way to read start reading the colour bands.

  1. There are five bands.
  2. There are very few cues which way to read it. Sometimes there is a larger gap between the multiplier and tolerance band. If there is cue, it is that brown and black bands have a narrower gap than other bands, and black and green bands have slightly larger gap.
  3. Since gold can never be the second band, it is wrong to read it from right to left, so it must be read from left to right.
  4. Since it has 5 bands, we can try standard 5-band decoding, from left to right. Bands brown-black-green-gold-green could mean 105 (the value or mantissa bands) with gold as exponent/multiplier band of 0.1, to end up with 10.5 ohms resistor, with the green band indicating 0.5% tolerance. Such a resistor value is included in E48, E96 and E192 series, and E192 series should have 0.5% tolerance.
  5. So 5-band decoding seems valid, but if measurement says it's near 1 megaohms, and depending on what the resistor does in the circuit, it might be clear whether it makes more sense for it to be 10.5 ohms or 1 megaohms. The 0.5% tolerance is also very suspicious for a generic circuit.
  6. To validate, on closer inspection, if the larger gap between black and green bands could be considered as separator between value bands and multiplier band, it would mean this might after all be a 4-band resistor with extra band for indicating some special purpose.
  7. 4-band decoding of brown-black-green-gold will decode to 10 (value/mantissa bands) with green band giving exponent/multiplier of 100000, or 1.0 megaohms, with gold indicating 5% tolerance. Much reasonable assumption, after all the multimeter says a value within 2% of that. Again such a resistor does exist in the resistor E series of standard values.
  8. Again what the resistor does in the circuit, it might make sense for it to have good temperature stability. And 4-band resistors with a fifth band for defining temperature stability do exist. And green is a valid colour for defining temperature stability. There are also resistors with manufacturer defined colour coding, and the fifth band could mean anything, which can be only figured out if the manufacturer of the resistor and resistor model is known, to find the datasheet for the resistor.

So, as verified with multimeter measurements, it really is a 4-band resistor with an extra fifth band. It means from left to right, it has two value/mantissa bands, one multiplier/exponent band, one tolerance band, and the extra band.

The brown-black bands mean 10, green band means to multiply by 100k, gold band means 5% tolerance, and the extra green band means the resistor is of some special type which may be manufacturer specific.

So it should not be read as 10.5 ohms but 10*10^5 ohms.

For example, the green band might mean a temperature coefficient of 20 ppm/K, or that it is a fusible resistor, or some indication of specific level of reliability.

So the problem is, if you don't know what the resistor does in a circuit or why it must have some special properties, don't simply change it to a standard resistor, because it might cause issues with the safety or operation of the device.

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