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Resistor Color Code Question

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Balaur:
Hello everybody,

I was dismantling some boards recovered from a large computer monitor and I have found a few color-coded resistors.

Since I'm somewhat proud in being able to manually decode 4/5-ring values, including tolerance, I was a bit perplexed by a few resistors following a non-standard code.

Example:

* Yellow-Violet-Red-Gold-Black

If you read the value as a standard 4-ring code, it's a 4K7, 5% resistor. Measurement seems to indicate that this is indeed the case.
Fair enough, but what's the black ring for? It's not a valid color for neither Temperature Coefficient or Fail Rate
There are several other resistors in this case, with a last black ring.

* Brown-Black-Gold-Gold-White

It's a 1R, 5% resistor, but the white ring should not be used there. Again, there are several resistors with a last white ring.

* Brown-Gray-Black-Silver-Brown

At least the 5-ring code it's valid: a 1R80, 1% resistor, but the 1R80 is a non-standard 1% (E96) value (measured OK).
I know that the manufacturers can produce any value they want, but come on.

So, do you have any insight to shed on these facts? One explanation could be that the resistors are manufactured according to the end user specifications, including value, tolerance and whatever the last ring means.

Thank you very much,
Dan

orbiter:
Being a noob myself and having newly learned resistor ident skills I'm interested too. The way I see it is... The fourth band (which can be silver or gold) is the standard multiplier (Gold = x0.1 Silver = x0.01)
The fifth band would still be the tolerance value (although the black and white ones are throwing me also) Are you sure the fifth band colours are correct and not discoloured or something?

John

DJPhil:

--- Quote from: Balaur on November 02, 2010, 01:34:19 pm ---
* Yellow-Violet-Red-Gold-Black

If you read the value as a standard 4-ring code, it's a 4K7, 5% resistor. Measurement seems to indicate that this is indeed the case.
Fair enough, but what's the black ring for? It's not a valid color for neither Temperature Coefficient or Fail Rate
There are several other resistors in this case, with a last black ring.

--- End quote ---
There is a vaild tempco for a black band, 250ppm/K. It doesn't seem to be listed often, as it's pretty crummy.
It's also a valid tolerance, +/-20% (last table on the page), when it shows up as a fourth band.

--- Quote from: Balaur on November 02, 2010, 01:34:19 pm ---
* Brown-Black-Gold-Gold-White

It's a 1R, 5% resistor, but the white ring should not be used there. Again, there are several resistors with a last white ring.

--- End quote ---
This one gets a bit arcane. I found a few references in google books to 'military reliability' bands in the fifth slot.
The orange 0.01/1khrs failure rate is said to be certified for missile electronics.
The yellow 0.001/1khrs failure rate is said to be certified for space flight systems.
The white band seems to indicate 'solderable leads'. Huh? Beats me.

--- Quote from: Balaur on November 02, 2010, 01:34:19 pm ---
* Brown-Gray-Black-Silver-Brown

At least the 5-ring code it's valid: a 1R80, 1% resistor, but the 1R80 is a non-standard 1% (E96) value (measured OK).
I know that the manufacturers can produce any value they want, but come on.

--- End quote ---
Oddly, this one would be valid as an 18R 5% with a 1/1khrs tested failure rate. Of course if you measured it at 1R8 then you've interpreted it correctly, but it just goes to show how messy these codes get.

Hope that helps. :)

orbiter:
Nowhere in my books did it say anything like that DJ :)

Thanks though, very interesting.

John

Balaur:

--- Quote from: DJPhil on November 02, 2010, 02:57:09 pm ---There is a vaild tempco for a black band, 250ppm/K. It doesn't seem to be listed often, as it's pretty crummy.
It's also a valid tolerance, +/-20% (last table on the page), when it shows up as a fourth band.

--- End quote ---

Very good finding about the black tempco. I fail basic internet search. I've looked everywhere *except* Wikipedia and didn't found the value for the black ring.
Thank you very much.

--- Quote from: DJPhil on November 02, 2010, 02:57:09 pm ---

--- Quote from: Balaur on November 02, 2010, 01:34:19 pm ---
* Brown-Gray-Black-Silver-Brown

At least the 5-ring code it's valid: a 1R80, 1% resistor, but the 1R80 is a non-standard 1% (E96) value (measured OK).
I know that the manufacturers can produce any value they want, but come on.

--- End quote ---
Oddly, this one would be valid as an 18R 5% with a 1/1khrs tested failure rate. Of course if you measured it at 1R8 then you've interpreted it correctly, but it just goes to show how messy these codes get.

Hope that helps. :)

--- End quote ---

Yes, the resistor is a 1R80. I've also measured that on a 4W lab multimeter and it showed a very nice 1.799? value.

Thank you all very much,
Dan