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 radioelements. Exceeding the permissible values โโof electricity leads not only to burnout of radio components, it happens that even current paths of the printed circuit board burn out. To restore functionality, it is necessary to calculate which components of the circuit are affected. Therefore, there is a way to check the resistor with a multimeter, as well as other radio components.
What is a radio element check?
Verification of radioelements is nothing but the measurement of their actual indicators and comparison with technically incorporated parameters during manufacture. If the data matches or is close in value (within acceptable limits), this indicates the serviceability of the radio components. In the event of a significant discrepancy, the elements are clearly defective and require replacement.
What results can be achieved by measuring the details of the radio circuit:
- Identify a malfunction. This will allow you to restore the circuit after replacing the burned element with a new one.
- Detect partial wear of the radio component. This will further help prevent the device from malfunctioning.
- Identify a hidden defect. For example, a poorly soldered terminal that will come off over time, especially if the circuit is exposed to vibration.
- Establish 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 device does the resistor test for?
A resistor, or resistance, is one of the main radio elements that is necessarily present in any circuit. It limits the current strength, dissipates excess power, it removes the voltage drop for the electronic keys to work, it performs a protective function (works on the principle of a fuse).
Among these devices, the most common are analog (arrow) and digital multimeters. When determining the parameters of the first type of equipment, in addition to the limits of measurement switching, a graduated scale for an ohmmeter is used. The use of electronic devices is a way to easily check a resistor with a multimeter. They display the reading on a digital display.
You can see in the photo presented how to check the resistor with a multimeter.
How to check the resistor rating?
Typically, a marking is applied to the radio elements, which tells the installer or repairman about the purpose of the device and its technical parameters. On resistors it can be digital or color coding. But sometimes there is absolutely no information on the element itself and on the printed circuit board, and to determine the rating of the device, in this case it is not clear how. To check the resistor with a multimeter in this case is the only possible option.
It is more convenient to use an electronic device of the DT830B type for these purposes. It is important to know that it is impossible to carry out reliable measurements of the value of a resistor if it is included in the circuit. The reason is the property of current flowing along the path of least resistance. And if a workaround for him comes across the circuit, bypassing the measured element, then the device will have anything but reliable information. Another reason why the element should be soldered is the presence of field parts in the circuit that may fail during the measurement process.
How to check the resistor with a multimeter in the circuit? To dissolve at least one of its conclusions. After that, you can conduct the measurement process:
- Test probes are connected to the device, black to the COM terminal, red to VฮฉmA.
- Move the mode knob to the largest position in the ฮฉ position.
- Connect the leads to the test leads (it is advisable not to do this by pressing the contacts with your fingers).
- 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 neighboring lower measurement limit, it makes sense to switch the instrument to it in order to more accurately obtain readings.
How to check a variable resistor with a multimeter?
The rating of the variable resistor is affixed to it, and the device itself has three outputs. The nominal value is the value between the extreme terminals of the radio element, the average output indicator will change in accordance with the angle of rotation of the adjustment 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 when turning the handle.
The variable resistor also needs to be evaporated from the circuit. After this is done, the measurement steps are as follows:
- Set the measurement limit of the multimeter to a position above the value of the rating indicated on the case.
- Measure readings between the extreme conclusions. If the resistance is infinity, the resistor is cut off, if zero, the element burns out. If the measurement results match, check the operation of the average output.
- The resistor adjustment knob is moved to any extreme position, one of the probes of the device is left at the extreme terminal, the other is connected to the middle one. The device should show a resistance close to zero or the nominal value (depending on the connection side) - this is correct. If the resistance is equal to infinity, then there was a break with the slider of the middle output. This is an indicator of how to check the health of a resistor with a multimeter.
- Next, determine the degree of wear of the resistive surface under the slider. To do this, without turning off the device, slowly turn the adjustment knob from one extreme position to another. In this case, follow the indications on the scoreboard - the resistance should smoothly change. If there is a loss (on the device corresponds to infinity), then the resistive layer is partially developed, and the radio element must be replaced.
How to check the resistor with a multimeter for serviceability?
As a rule, the device does not check all elements in a row, but those that cause suspicion. They may be darkened, with signs of peeling paint and other visible irregularities. To reliably determine whether the radio component is working or not, you need to:
- Measure the resistor rating and compare with the declared value on the case. The deviation of the readings shall not exceed the permissible percentages, which are also indicated on the element.
- Having connected probes, it is necessary to slightly move the conclusions of the radio element. If the readings suddenly begin to disappear, then appear, this is a sure sign of a hidden defect.
How, without evaporating, check the resistor in the circuit?
There are resistors that come with conclusions, there are leadless SMD elements. It is difficult to solder the last from the printed circuit board without a special nozzle on the soldering iron. Therefore, the parameters of such radio components are measured directly in the circuit. How to check the resistor with a multimeter without evaporating:
- Carefully inspect the printed circuit board and find on it a track extending from any output of the SMD resistor without branches.
- Gently cut it in a place with the smallest 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 in the place of the gap.
How to determine the permissible measurement error?
On the case of each resistor there is information about the deviations of the nominal. It can be registered as 5%, 10%, 20% or hidden in color coding. For a normal operational radio element, when measuring its face value, the readings will not go beyond the permissible percentage.
Conclusion
Itโs easy to figure out how to check the resistor with a multimeter, but you should not climb into complex devices containing many chips with the device. It is much cheaper in this case to entrust the work to an experienced master.