Resistor Color Code Question - Page 1
Forum section: electronics / beginners

author: Balaur
author_rank: Unknown
timestamp: November 02, 2010, 01:34:19 pm
content: 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-BlackIf 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 RateThere are several other resistors in this case, with a last black ring.Brown-Black-Gold-Gold-WhiteIt'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-BrownAt 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

author: orbiter
author_rank: Frequent Contributor
timestamp: November 02, 2010, 02:52:48 pm
content: 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

author: DJPhil
author_rank: Frequent Contributor
timestamp: November 02, 2010, 02:57:09 pm
content: Quote from: Balaur on November 02, 2010, 01:34:19 pmThere is availd tempco for a black band, 250ppm/K. It doesn't seem to be listed often, as it's pretty crummy.It's also avalid 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 pmThis 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 pmOddly, 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.

author: orbiter
author_rank: Frequent Contributor
timestamp: November 02, 2010, 03:02:19 pm
content: Nowhere in my books did it say anything like that DJThanks though, very interesting.John

author: Balaur
author_rank: Unknown
timestamp: November 02, 2010, 04:32:38 pm
content: Quote from: DJPhil on November 02, 2010, 02:57:09 pmVery 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 pmYes, 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

author: Zero999
author_rank: Super Contributor
timestamp: November 02, 2010, 06:06:51 pm
content: Because the E24 series doesn't match with the E92 series, the E24 series is also available in narrower tolerances than 5%.In my opinion, they should've designed it so the E96 is just an extension of the E24 series.

author: Neilm
author_rank: Super Contributor
timestamp: November 02, 2010, 08:04:03 pm
content: There are occasions when a designer will require some really weird value resistors. I have had to use values like 1.8 ohms on occasion. Usually I buld them up out of standard parts, but occasionally I need special resistance value at a tight tolerance, good voltage rating or maybe I don't have room to put multiple resistors on the PCB.Neil

author: Zero999
author_rank: Super Contributor
timestamp: November 02, 2010, 08:18:51 pm
content: Series/parallel is normally fine.I can't say I've have ever had that problem, as for most circuits it's the ratio that's important rather than the resistance so getting the right ratio of E24 and E96 values is normally easy.

author: Neilm
author_rank: Super Contributor
timestamp: November 03, 2010, 07:27:13 pm
content: Quote from: Hero999 on November 02, 2010, 08:18:51 pmTrue, but I have had some reasonably specialist applications when the exact value was important. Generally these happen in precision measurement circuits.Neil