Wirewound Resistor Color Code
Terina
Here we identify the color code determining the values of non-inductive wire wound resistors, specifically Yageo's NKN series (but applicable to other manufacturers of this class), which are a unique and separate case recognizable by a final black stripe, NOT TO BE CONFUSED WITH CASES OF normal 3 or 4 BAND RESISTORS WITH AN ADDED TEMPERATURE COEFFICIENT BAND, which are then often wrongly interpreted/read as 4 or 5 band resistors respectively, as is the case in the answer of which my question was wrongly deemed a duplicate of!
The non-inductive resistors treated in this question use a unique color coding scheme which differs greatly from the standard code, and as this issue has never been raised on Stack Exchange or the internet at large, it is valuable to present an explanation of its recognition and interpretation, as it is otherwise almost impossible to find information about them.
I was just disassembling an Asus 19 V, 4.74 A laptop SMPS power brick, and came across these two resistors. I am at a loss as to their values, as neither seem to follow the standard color code we all know and love. Both test 0.0 or 0.1 Ω on my multimeter, and both look brand spanking new, no burn marks, and the power supply works a treat.
My guess is that these are some kind of fancy current sensing resistors, with super low resistances (the standard color code doesn't allow for anything lower than 0.01 Ω). Has anyone of you kind folks seen something like this before, and could maybe explain the code for this type of niche resistor?
So after much searching and some great advice from @evildemonic I managed to find a datasheet with an updated/more detailed table of the resistor color code markings. Our guess is that these are Yageo NKN series wire-wound non-inductive resistors (available E24 0.03-220 Ohm, 1-7W), 1W type. Now that datasheet says these should have a green colored body, and these are grey, but some show the Yageo ones in grey too, so whatever, even if they are clones, they follow this numbering scheme. The defining characteristic is a final black band, indicating non-inductive (and not a temperature coefficient marking, as these are 300ppm/K, a class that doesn't exist in the traditional marking scheme, black would otherwise be 100/200/250 ppm/K depending on who you ask). I figure some other companies might also use this scheme for 'ultra' low value resistors (anything lower than 0.01 Ohm or requiring a further decimal in the tens of miliohms). One other thing I've seen is also pink as the 0.001 multiplier, in some other companies datasheet, just to give you an idea if you're picking your brain deciphering some odd looking resistor.
In the context of the repair of European audio and video gear, made by companies like Grundig or Philips, I come across "safety" resistors every once in a while, i.e. flameproof or fusible resistors. They are often marked in the schematic like this:
Note: This is just a temporary fix. The replacement part I used to bridge the defective resistor will likely fail prematurely. On the other hand, using a large 1...4 Watt resistor will last forever, but it will fail to protect the unit and I might create a fire hazard. This is just a temporary fix to check if the rest of this particular CD player still works (it does).
I would like to replace the resistors with the closest possible match. However, the service manuals often don't say what exact manufacturer or type they used, and I had no success finding data sheets by some of the companies that come to mind (Vishay, Beyschlag, BC components, ...)
White or black rings on more modern and often larger fusible resistors are common in today's switching power supplies etc., but any sources with data for safety resistors with yellow, orange or violet rings would be greatly appreciated.
Blue body, yellow fifth band: Firstohm FGE. Link to distributor for the catalog, because the individual data sheet from the manufacturer is only available upon request.The data sheet does not state the marking code, so we have to rely on the picture for the type/series on their website.
Pink body, black fifth band: Firstohm SCP. Link to distributor for the catalog, because the individual data sheet from the manufacturer is only available upon request.The data sheet does not state the marking code, so we have to rely on the picture for the type/series on their website.
Note (1): Firstohm uses a blue fifth band to mark high voltage resistors. For small types like 0207 especially, high voltage resistors will have high resistance values (above 100 kOhm, mostly above 1 MOhm) while fusible resistors will have low values (below 1 kOhm, mostly below 100 Ohm).
Note (2): The data sheets are not easily available for download from their website, there are no specifications for the marking codes, but hey - if you enjoy fancy artwork instead, they certainly have some on-topic stuff in their catalog, boom!
Note: KOA also has surge-rated resistors, they have a blue/grey body with a fifth band in black, green or white. Another example why one must check the footnotes and think about the application when replacing a special-purpose resistor. My favorite chemistry teacher once taught me that "one can do anything if one knows what they're doing". In the context of repair work: Fix anything, but know what you're doing. (And you won't cause someone's house to burn down.)
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An electronic color code or electronic colour code (see spelling differences) is used to indicate the values or ratings of electronic components, usually for resistors, but also for capacitors, inductors, diodes and others. A separate code, the 25-pair color code, is used to identify wires in some telecommunications cables. Different codes are used for wire leads on devices such as transformers or in building wiring.
In the 1920s,[citation needed] the RMA resistor color code was developed by the Radio Manufacturers Association (RMA) as a fixed resistor coloring code marking. In 1930, the first radios with RMA color-coded resistors were built.[1][2] Over many decades, as the organization name changed (RMA, RTMA, RETMA, EIA)[3] so was the name of the code. Though known most recently as EIA color code, the four name variations are found in books, magazines, catalogs, and other documents over more than 94 years.
Color bands were used because they were easily and cheaply printed on tiny components. However, there were drawbacks, especially for color blind people. Overheating of a component or dirt accumulation may make it impossible to distinguish brown from red or orange. Advances in printing technology have now made printed numbers more practical on small components. The values of components in surface mount packages are marked with printed alphanumeric codes instead of a color code.
Precision resistors may be marked with a five band system, to include three significant digits, a power of 10 multiplier (number of trailing zeroes, and a tolerance band. An extra-wide first band indicates a wire-wound resistor.[6]
Zero ohm resistors, marked with a single black band,[10] are lengths of wire wrapped in a resistor-like body which can be mounted on a printed-circuit board (PCB) by automatic component-insertion equipment. They are typically used on PCBs as insulating "bridges" where two tracks would otherwise cross, or as soldered-in jumper wires for setting configurations.
The "body-end-dot" or "body-tip-spot" system was used for cylindrical composition resistors sometimes still found in very old equipment (built before the Second World War); the first band was given by the body color, the second band by the color of one end of the resistor, and the multiplier by a dot or band around the middle of the resistor. The other end of the resistor was in the body color, silver, or gold for 20%, 10%, 5% tolerance (tighter tolerances were not routinely used).[11][12][13][14]
Capacitors may be marked with 4 or more colored bands or dots. The colors encode the first and second most significant digits of the value in picofarads, and the third color the decimal multiplier. Additional bands have meanings which may vary from one type to another. Low-tolerance capacitors may begin with the first 3 (rather than 2) digits of the value. It is usually, but not always, possible to work out what scheme is used by the particular colors used. Cylindrical capacitors marked with bands may look like resistors.
Extra bands on ceramic capacitors identify the voltage rating class and temperature coefficient characteristics.[11] A broad black band was applied to some tubular paper capacitors to indicate the end that had the outer electrode; this allowed this end to be connected to chassis ground to provide some shielding against hum and noise pickup.
A similar six-dot code by EIA had the top row as first, second and third significant digits and the bottom row as voltage rating (in hundreds of volts; no color indicated 500 volts), tolerance, and multiplier. A three-dot EIA code was used for 500 volt 20% tolerance capacitors, and the dots signified first and second significant digits and the multiplier. Such capacitors were common in vacuum tube equipment and in surplus for a generation after the war but are unavailable now.[17]
Standards IEC 60062 / EN 60062 do not define a color code for inductors, but manufacturers of small inductors use the resistor color code, typically encoding inductance in microhenries.[18] A white tolerance ring is used by TDK to indicate custom specifications.[18]
Power transformers used in North American vacuum-tube equipment were often color-coded to identify the leads. Black was the primary connection, red secondary for the B+ (plate voltage), red with a yellow tracer was the center tap for the B+ full-wave rectifier winding, green or brown was the heater voltage for all tubes, yellow was the filament voltage for the rectifier tube (often a different voltage than other tube heaters). Two wires of each color were provided for each circuit, and phasing was not identified by the color code.
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