Learning to do you own appliance repair can save you money in two ways. You save money by not having to pay the $50 to $75 an hour labor rate that most service technicians charge, with a one hour minimum. In some case, you will even save big bucks on parts. For example, today's major appliances use a lot of electronic circuitry mounted on PC (Printed Circuit) boards. The problem with that is that service technicians do not repair those boards, they replace them. The problem with that is that a major board i.e. the temperature controller for an electric range, might cost $175 when the only thing wrong with it is a bad resistor or capacitor that you could buy for $0.50 to $1.00 from any Radio Shack store or similar electronics parts store. Since the color codes for each component is slightly different, we will take each of them up in their own article. We will be concentrating on the resistor color codes in this article.
There will be many skill sets that you will have to learn to troubleshoot at the component level. One of the most important skill sets that you will have to master is working with color codes. There are color codes for resistors, color codes for capacitors, color for transformers and other inductors. There are color codes for wiring and many other color codes to learn, but two of the ones you will encounter most often are the ones for resistors and capacitors so we will cover them in detail in this article.
Contrary to what many think, color codes were not created to make things difficult for the technician, they were created out of necessity. It was much easier to place color bands on tiny components than it was to stamp legible number on them. If you are familiar with the physical size of a 1/4-Watt carbon resistor, you know what I mean. For those who are not familiar with how tiny 1/4-Watt carbon resistors are, here is a picture of some common wattage resistors and a ruler to compare them by.
Radio Manufacturers Association.
The color codes used on electronic components was developed during the early 1920 by the Radio manufacturers Association, the RMA. As time passed and new electronic technology were developed, the RMA changed its name to keep pace. In 1950, the RMA became The Radio Television Manufacturers Association (RTMA). Then, again it changed it name in 1953 to the Radio Electronic Television Manufacturers Association (RETMA). In 1957 it became the Electronics Industries Association (EIA). In 1997 it changed its name for the last time when it became the Electronics Industries Alliance (EIA).
The resistor color code that we still use today was first published as the EIA-RS-279 Standards. Later it was adopted as the International Standard and published as the IEC 60062.
The first key to remembering and using this color code is remembering the order in which the color appear. Back in the day when I built my first real radio from a schematic I found in an electronics magazine, I was nine or ten at the time, I learned this color code by rote memorization. Since then I have discovered a neat little Mnemonic that will make it easier for you to memorize it.
Bad beer rots our young guts but vodka goes well – get some now
Where Bad = Black
beer = Brown
rot = Red
orange = Orange
young = Yellow
guts = Green
but = Blue
vodka = Violet
goes = Gray
well = White
get = Gold
some = Silver
now = None
Applying the color code to a resistor.
A resistors color code is read beginning at the left end of the resistor's body. The ends of the resistor are identifiable by the wider space between the last two color bands or by the wider distance between the last band and the end of the resistor's body. The latter applies when there is no tolerance band such as on 20% resistors.
The first and second colored bands represent the first and second significant figures in the resistors value in Ohms. In the example I provided here, the Red band represents 2 and the Violet represents 7, so the first two significant figures in the value of the resistor is 27.
The third colored band is the “Multiplier “ band and designates how many zeros must be added after the first two significant figures in the value. In our example, the Green represents 105, or 10 to the 5th power. In plain English that simply means that you add five zeros after the second significant figure which gives our sample resistor a value of 2,700,000 Ohms.
As a refresher for those who may be a little rusty in the math department, the following table shows you what to multiply the first two significant figures by to get the final value of the resistor's value in Ohms.
Our example resistor could also be said to have a value of 2.7 Mega-ohms or 2.7M. As you can see from this table we give each of the powers of ten notations that I described above a metric name and use those designations when talking about electrical quantities. You may want to copy and print out these charts and tables for future reference because we will be using them repeatedly as you progress through these articles.
For resistors you will be dealing with Unit, Kilo, and Mega values.
The fourth colored band, when there is a fourth band on the resistor is the tolerance band. The Gold and Silver bands represent a tolerance of 5% and 10% respectively. A resistor that has no tolerance band has a tolerance of 20%. What tolerance means is that the resistor may + or – that percentage of its indicated value and still be considered good.
The resistors wattage rating.
One of the things that the color code does not cover is a resistors wattage rating. The wattage of a resistor is a critical consideration when replacing one in a circuit because it specifies how much power it can safely handle. With carbon resistors, the power rating is indicated by its physical dimensions good design practice dictates that you use a resistor capable of dissipating at least 1.25 times the power actually generated in the circuit. To compute the wattage rating of a resistor simply multiply the voltage being dropped across it by the current flowing through it. For example if there was 50 Volts being dropped across a resistor with 0.01 Amperes flowing through it we would multiply 50 X 0.01 and get 0.5 Watts. Using good design practices, we would then multiply that 0.5 Watts by 1.25 to get 0.625 Watts which means we would use a 1.0 Watt resistor in this circuit.