Our today's video is about capacitance measurements. Not just regular capacitance measurements but measurements without desoldering capacitors from a PCB.
During the past several years different internet marketplaces are offering various devices that can measure capacitance and other parameters of capacitors without desoldering them from a PCB.
There are many discussions on different forums, some people buy them, some people don't, some share experiences. Personally, I am interested in two questions. First of all, the manufacturer lists never include well-known brands like FLUKE, APPA, UNI-T, MASTECH, etc., are never present in manufacturer lists. So, none of the trusted brands produce such devices. And the second question is strictly technical, it's based on elementary knowledge of school physics. At school we were taught that if two capacitors are connected in parallel, their equivalent capacitance will be equal to the sum of their individual capacitance. If in series, then we have a more complicated formula. We have to deal with inverted values, so 1/C = 1/C1 + 1/C2.
Here we have a PCB and we want to measure capacitance of this capacitor. Its contacts are right here. When we connect a multimeter, or another device that measures capacitance, to those contacts, we will obtain a value of the actual capacitance only if one single element, this capacitor, is soldered between those two points. There is not one element on the PCB, there are more than a hundred. Therefore, capacitance between those two points will be equal to some equivalent value, which is not that easy to calculate. This is why, even theoretically, based on the knowledge of school physics, it's not possible to measure capacitance of an element without desoldering it from a PCB. But enough of theory, let's move on to practice.
We will conduct a number of measurements on this PCB. As you can see, it has many different components: electrolytic capacitors, SMD capacitors, inductors, resistors, microchips, light-emitting diodes – a whole package. We will conduct measurements in several steps. I have already completed the first step – I have written down all of the nominal capacitance values in the points where measurements will be taken. There's one exception: there is no capacitor in point 5, as it has been previously removed. Out of curiosity, we will measure capacitance in this point as well. In the second step I will measure capacitance in those points without desoldering the capacitors. In the third step I will desolder all capacitors, measure their capacitance in a normal way and record the values. We will compare them and find a result.
In this video I have shown you that measuring capacitance without desoldering capacitors from a PCB is a myth.
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