Electronic circuits sometimes fail. There are many reasons for this, but the point is to change the current modes, which have a destructive effect on the radio elements. Exceeding the permissible ratings of electricity leads not only to the burnout of radio components, it happens that even the current-carrying tracks of the printed circuit board burn out. To restore operability, it is necessary to calculate which components of the circuit have suffered. Therefore, there is a way to check the resistor with a multimeter, as well as other radio components.
What is radio check?
Checking radio elements is nothing more than measuring their actual performance and comparing them with the technically embedded parameters during manufacture. If the data match or are close in value (within acceptable limits), this indicates the he alth of the radio components. In the event of a significantdiscrepancies, the elements are clearly defective and require replacement.
What results can be achieved by measuring the details of the radio circuit:
- Find the problem. This will allow you to restore the circuit after replacing the burnt element with a new one.
- Detect partial wear of a radio component. This will help prevent device failure in the future.
- Reveal a hidden defect. For example, a poorly soldered lead that will come off over time, especially if the circuit is subjected to vibration.
- Set up a chain of violations for one failed radio component. In many schemes, the combustion of one particular element automatically leads to the combustion of others dependent on it.
What instrument is used to test resistors?
Resistor, or resistance, is one of the main radio elements, which is necessarily present in any circuit. It limits the strength of the current, dissipates excess power, removes the voltage drop from it for the operation of electronic keys, it performs a protective function (it works like a fuse).
Among such devices, the most common are analog (pointer) and digital multimeters. When determining the parameters of the first type of equipment, in addition to the measurement switching limits, they use a graduated scale for an ohmmeter. The use of electronic devices is the easiest way to check the resistor with a multimeter. They display the value of the readings on a digital display.
You can see on the presented photo how to check the resistor with a multimeter.
How to check the value of a resistor?
Usually, radio elements are marked, which tells the installer or repairman about the purpose of the device and its technical parameters. On resistors, this can be a digital or color coding. But sometimes there is absolutely no information on the element itself and on the printed circuit board, and it is not clear how to determine the value of the device, in this case. Checking the resistor with a multimeter in this case is the only option.
It is more convenient for these purposes to use an electronic device such as DT830B. It is important to know that it is impossible to make reliable measurements of the resistor value if it is included in the circuit. The reason for this is the property of current to flow along the path of least resistance. And if there is a workaround for it in the circuit, bypassing the element being measured, then the device will have anything, but not reliable information. Another reason why you should desolder the element is the presence of field parts in the circuit, which can fail during the measurement process.
How to check a resistor with a multimeter in a circuit? Solder at least one of its conclusions. After that, you can carry out the measurement process:
- Measuring probes are connected to the device, black to the COM terminal, red to VΩmA.
- Rearrange the mode change knob to the Ω position to the largest limit.
- Connect the leads to the test leads (it is advisable not to do this by pressing the contactsfingers).
- A number will appear on the screen, which will correspond to the value of the resistor. If this reading does not go beyond the value of the adjacent lower measurement limit, it makes sense to switch the device to it in order to obtain more accurate readings.
How to test a variable resistor with a multimeter?
The value of the variable resistor is marked on the case, and the device itself has three outputs. The nominal value is the value between the extreme terminals of the radio element, the indicator of the average output will change in accordance with the angle of rotation of the adjusting knob. In order not to "anyhow" check the variable resistor with a multimeter, it is not enough to measure its value. It is important to see the nature of the change in resistance between the middle terminal relative to the extreme one when you turn the knob.
The variable resistor also needs to be soldered out of the circuit. After this is done, the measurement steps are as follows:
- Set the measurement limit of the multimeter to a position higher than the nominal value indicated on the case.
- Measure the readings between the extreme conclusions. If the resistance is equal to infinity, the resistor is broken; if it is zero, the element burns out. If the measurement results correspond to the nominal value, the operation of the middle output is checked.
- Move the resistor adjustment knob to any extreme position, one of the probes of the device is left at the extreme output, the other is connected to the middle one. The device should show a resistance close to zero or nominal (dependingfrom the connection side) is correct. If the resistance is equal to infinity, then there was a break with the middle output slider. This is an indicator of how to check the he alth of the resistor with a multimeter.
- Next, the degree of wear of the resistive surface under the slider is determined. To do this, without turning off the device, slowly turn the adjustment knob from one extreme position to another. At the same time, they monitor the readings on the scoreboard - the resistance should change smoothly. If disappearances occur (on the device it corresponds to infinity), then the resistive layer is partially worn out, and the radio element needs to be replaced.
How to check the resistor with a multimeter for serviceability?
As a rule, not all elements are checked with the device, but those that are suspicious. They may be darkened, with traces of peeling paint and other visible violations. To reliably determine whether the radio component is working or not, you need:
- Measure the value of the resistor and compare with the declared value on the case. The deviation of the readings should not exceed the allowable percentages, which are also indicated on the element.
- Having connected the probes, it is necessary to slightly move the conclusions of the radio element. If the readings suddenly start to disappear, then appear, this is a sure sign of a hidden defect.
How, without soldering, to check the resistor in the circuit?
There are resistors that come with leads, there are leadless SMD elements. Solder the last ones out of the printedThe board is difficult without a special nozzle for a soldering iron. Therefore, the parameters of such radio components are measured directly in the circuit. How to test a resistor with a multimeter without soldering:
- Carefully inspect the circuit board and find a track on it extending from any terminal of the SMD resistor without taps.
- Carefully cut it in the place with the least thickening.
- Measure the radio element with the device.
- After checking the resistor with a multimeter on the board, and it turned out to be faulty, replace it and solder the jumper at the break.
How to determine the allowable measurement error?
On the case of each resistor there is information about the nominal deviations. It can be written as 5%, 10%, 20% or hidden in color coding. For a normal serviceable radio element, when measuring its face value, the readings will not go beyond the allowable percentage.
Conclusion
It's easy to figure out how to test a resistor with a multimeter, but you shouldn't get into complex devices containing many microcircuits with the device. It is much cheaper in this case to entrust the work to an experienced master.
