The use of multilayer printed circuit boards, the reduction of tracks, contact pads leads to the fact that it becomes more and more difficult to solder the elements for replacement. There are several ways to check the performance of capacitors directly on the board.
Difficulties in checking a capacitor
When measuring the capacitance of a capacitor on a board without first dismantling, problems arise. The capacitor is always included in the circuit and can be adjacent to other circuit elements on the board. Especially affect the measurement of the capacitance of the winding of transformers, inductance, fuses - they have a small resistance to direct current.
Therefore, it is necessary to make sure that there is no influence of such elements in the circuits of the measured capacitor. If a transistor or a diode is included in circuits with a capacitor, then during measurement you can see the deflection of the arrow to a certain position and drop to a certain value equal to the resistance of the semiconductor junctions. And if there is no short circuit, then the capacitor may be serviceable.
Checking the capacitor with a multimeter
When touched by the probes of the multimeter, a direct current from the tester is supplied to the capacitor. The capacitor will charge and the resistance will gradually increase.
On an electronic tester, the value will rise from negative or positive numbers to one, indicating a resistance greater than the range selected by the selector knob. After rearranging the tester probes in places, the capacitor must recharge, the device must act in the same way.
By the deviation of the arrow of the pointer multimeter when connecting the capacitor and returning it to its original position, you can see the maximum deviation on the scale.
If you swap the tester probes, the instrument needle should again deflect to the maximum and smoothly fall to its original position. After that, it is necessary to take a similar and obviously working capacitor, and if the tester arrow on the control element deviates more, then the tested capacitor is inoperative.
If, when measuring and matching the pros and cons on the tester and the terminals of the capacitors, the device shows resistance, then such a capacitor is faulty.
Checking the capacitor with other devices
There are devices that allow you to check capacitors right on the board. Such devices operate at low voltages to reduce the risk of damage to other elements.
You can make your own prefix to the tester according to the diagrams published in magazines and on the Internet. But it is not always possible to take measurements with them precisely because of the influence of other elements of the circuits. For example, several capacitors installed in parallel will eventually show the total capacitance.
