Everyone who has been engaged in the repair of electronic equipment knows that sometimes it is necessary to determine its value by the appearance of the resistor . The easiest way is to measure the resistance with an ohmmeter, but the trouble is, it is not always possible to solder it out without damaging the circuit board, especially the multilayer one, but it happens that there are doubts about the integrity of the internal contacts. If there is a circuit, everything is simple - you can look into it and see that R18 is, for example, 47 Ohms. And if it is not there, but you need to figure it out, and you will have to draw a diagram yourself?
Fortunately, manufacturers of electronic components have agreed among themselves, and there is a standard marking of resistors. True, and it has undergone changes over the past decades.
The most common in our time is the color marking of resistors. It is very simple, and to read the face value, holding a simple cardboard decoder, is a matter of seconds. This device is widely available, is in any radio store and is very cheap, so remember the color values ​​is not worth it. The marking of the resistors consists in the fact that rings of different colors are applied to the resistance with paint, each of which means a number, factor or degree of accuracy.
Strips are available from three to five. They should be read from the first, located closer to one of the conclusions. For example, four bands. The first is brown, the second is black, the third is red, the fourth is gray. You should dial these colors on the decoder, skipping the third (there you should select the “no” position). Done, this is 1 kOhm with an error of 0.05%. If there are three bands, the accuracy is 20%.
Sometimes it becomes necessary to deal with old Soviet equipment, which is still in use. Once they scolded her, she seemed clumsy and ugly, but time has shown the amazing vitality of some samples of this equipment, and now it is sometimes even called "vintage". The marking of Soviet-made resistors is even simpler than color, they simply write the value, for example, 4K7 means 4,700 Ohms. And that’s all. Simple and clear. One drawback is that this inscription may appear from below, Soviet radio plants very rarely used a “standing” installation of resistances, the Japanese liked this to save space on the board.
The miniaturization of electronic technology has confronted its manufacturers with the need to invent new installation methods. Classical soldering of resistors through openings on the board in the “standing” or “lying” position takes up too much space, and now a new method for assembling micro-boards - smd. In this English abbreviation, three words are encrypted: “surface” - surface, “mount” - installation, and “technology” - this is clear what it means. Small parts are soldered directly to the track on the surface, without holes or legs. It took a new labeling of the resistors, and other components, such as diodes and capacitors, too.
Marking smd resistors is somewhat reminiscent of the good old Soviet method. They also printed numbers and letters. There is still a difference. The letter is not always, if necessary, "R" is used as a separating comma.
For example, 2183 means that 218 needs to be multiplied by 1000, it turns out 218 kOhm. Resistances with a tolerance of up to 10% are marked with four digits, the latter means the degree to which you need to raise the ten, and multiply by this result the three-digit number formed by the first two digits.
A bit more complicated with smd resistors of higher quality, with a tolerance of 1%. Here the degree of tens is set by the letter, for example, D is 10 in a cube. If 10D is inscribed on the resistance, it means 10 kOhm.
In addition to the correspondence tables, the repairman will need a magnifying glass, since the symbols are very small!