Measuring capacitance without desoldering capacitors from a PCB - is it possible?

hello today we are going to be talking about measuring capacitance however we aren't going to be performing just any old capacitance measurements but measurements without desoldering capacitors from a PCB over the past several years different websites have offered various devices that measure capacitance and other details of capacitors without desoldering them from a PCB there's been lots of discussion on different forums some people say that they purchased them others don't recommend it etc all of these discussions raise two questions for me first of all why do the products listed never include well-known manufacturers like fluke app' unity mass tech etc that seems to imply that none of the most trusted brands produce any of this type of device the second question is strictly technical it's based on elementary knowledge of school physics at school we are taught that if two capacitors are connected in parallel their equivalent capacitance will be equal to the sum of their individual capacitances however if they are in a series then we have a more complicated formula we have to deal with inverted values so 1 divided by c equals 1 divided by c 1 plus 1 divided by c 2 here we have a PCB and we want to measure the 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 these two points here we have to remember that there's more within one element on the PCB in fact there are more than a hundred therefore the capacitance between these two points would be really hard to calculate this is why even theoretically based on the knowledge of school physics is not possible to measure the capacitance of an element without desoldering it from a PCB enough with theory though let's move on to the real world we will conduct an Eevee experiment with a number of different measurements on this PCB as you can see it has many different components electrolytic capacitors SMD capacitors inductors resistors microchips light-emitting diodes it has the works we will conduct our measurements in different phases I have already completed the first one by writing 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 five as it has been previously removed just for kicks we will measure the capacitance in this point as well in Phase two we will measure the capacitance of those points without desoldering the capacitors in Phase three I will decide are all capacitors measure their capacitance as usual and record the values we will then compare them to the original values and find a result let's begin we'll turn on the multimeter as you can see I chose a unity UT 139 C because it measures capacitance very well we also have another video about this so let's measure point 1 the capacitance is one hundred microfarads it's supposed to be 47 we already see an inconsistency point - let me try again somewhere close to 164 164 microfarads obviously its capacitance is significantly different from the value printed on the capacitor in point three we should have four hundred and seventy micro for ads however we get almost one militar at this is two times as high let's record this the capacitance should be 47 in point four and it's about 164 microphones in point five right here there's no capacitor but for the accuracy of the experiment let's measure it as well what can I say it looks like we have an invisible capacitor on the PCB with a capacitance of 58 micro farad's we should patent this technology I will also record zero in this slot as there is no capacitor here lastly point six we should have 100 microfarads let's see what we get sixty-six microphones this is the most accurate measurement so far with a thirty five percent error as you can see from this first step if we measure capacitance without desoldering capacitors from the PCB there is a big difference between the nominal or stated values and the measured values we will now disorder and measure them in a more correct way it is possible that some of the capacitors capacitance has changed over time capacitor number three number four there is no capacitor number five and number six this soldering iron tip is not very convenient for tasks like these a bigger one would have been better so I have D soldered the capacitors now let's measure their actual capacitance it looks like our multimeter has automatically switched off we will use a different test lead this time as the standard one is not convenient for this type of measurement that's because the capacitor leads are gone as you can see this one has a capacitance of 67 microphones and this one has 46 microphones the same as the value printed on the capacitor capacitor number three its capacitance should be 470 micro farad's 445 here it's 49 microphones and in our first or in this case our last capacitor with a printed value of 47 microphones and a measured value on the PCB of around 100 about 48 microphones the results speak for themselves the capacitance values are incorrect in every point except the last one but this is an exception to the rule rather than proof here we didn't even have a capacitor and we measured 58 microflora ads over here we had a stated capacitance of 47 microphones we measured it on the PCB at 164 and it turned out to actually be somewhere around 46 to 47 here the measured capacitance was almost twice as high as the actual one the same here with 164 microphones when it should have been 49 here we measured 100 microfarads in the PCB but it's actual capacitance is a mere 48 microphones so as we can clearly see the measurements that are in the second column are not measurements at all they are more like a lottery number from a fortune cookie some may say that I wasn't using a special RLC meter that measures ESR but regular multimeter instead first of all this multimeter measures capacitance very accurately as we have previously shown secondly what is ESR it's basically a series of resistances therefore no matter what you use for your measurements even if it's the best device for measuring capacitance you cannot measure the ESR of an individual capacitor instead you will end up measuring an equivalent value of the entire circuit many devices present themselves as tools that can measure capacitance without desoldering the elements of a PCB most of the descriptions written online have one main idea a small voltage is applied to these points in a way that supposedly doesn't affect anything surrounding them just this small area so this capacitor will not be affected anymore and it will not take part in the measurements but that's all bogus because it's impossible to measure this capacitor if there are a lot of other things here on the PCB you can measure anything else you want but not the capacitor actually you can measure an equivalent capacitance but not the capacitance of this particular capacitor by itself therefore do not buy these devices instead by regular quality multimeters you don't necessarily need this one even just make sure you buy regular measuring equipment from good manufacturers and measure things properly in this video I have shown you that measuring capacitance without desoldering capacitors from a PCB is a myth please like this video if you found it useful and subscribe to our Channel we hope you have a great day and take correct measurements

Channel: ToolBoom

Views: 202,857

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Id: tXxOHcUhVfE

Length: 13min 36sec (816 seconds)

Published: Wed Feb 03 2016