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

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Language: en

00:00:12.240
hello today we are going to be talking
00:00:14.610 00:00:14.620 about measuring capacitance however we
00:00:17.040 00:00:17.050 aren't going to be performing just any
00:00:18.510 00:00:18.520 old capacitance measurements but
00:00:20.099 00:00:20.109 measurements without desoldering
00:00:21.480 00:00:21.490 capacitors from a PCB over the past
00:00:23.820 00:00:23.830 several years different websites have
00:00:25.650 00:00:25.660 offered various devices that measure
00:00:27.089 00:00:27.099 capacitance and other details of
00:00:28.950 00:00:28.960 capacitors without desoldering them from
00:00:31.109 00:00:31.119 a PCB there's been lots of discussion on
00:00:33.479 00:00:33.489 different forums some people say that
00:00:35.520 00:00:35.530 they purchased them others don't
00:00:37.260 00:00:37.270 recommend it etc all of these
00:00:39.000 00:00:39.010 discussions raise two questions for me
00:00:41.010 00:00:41.020 first of all why do the products listed
00:00:43.350 00:00:43.360 never include well-known manufacturers
00:00:45.450 00:00:45.460 like fluke app' unity mass tech etc that
00:00:49.170 00:00:49.180 seems to imply that none of the most
00:00:50.790 00:00:50.800 trusted brands produce any of this type
00:00:52.770 00:00:52.780 of device the second question is
00:00:54.779 00:00:54.789 strictly technical it's based on
00:00:56.490 00:00:56.500 elementary knowledge of school physics
00:00:58.290 00:00:58.300 at school we are taught that if two
00:01:00.779 00:01:00.789 capacitors are connected in parallel
00:01:02.130 00:01:02.140 their equivalent capacitance will be
00:01:04.229 00:01:04.239 equal to the sum of their individual
00:01:06.179 00:01:06.189 capacitances however if they are in a
00:01:08.340 00:01:08.350 series then we have a more complicated
00:01:10.080 00:01:10.090 formula we have to deal with inverted
00:01:12.300 00:01:12.310 values so 1 divided by c equals 1
00:01:15.450 00:01:15.460 divided by c 1 plus 1 divided by c 2
00:01:17.850 00:01:17.860 here we have a PCB and we want to
00:01:20.340 00:01:20.350 measure the capacitance of this
00:01:21.780 00:01:21.790 capacitor its contacts are right here
00:01:23.969 00:01:23.979 when we connect a multimeter or another
00:01:26.070 00:01:26.080 device that measures capacitance to
00:01:27.780 00:01:27.790 those contacts we will obtain a value of
00:01:29.969 00:01:29.979 the actual capacitance only if one
00:01:32.039 00:01:32.049 single element this capacitor is
00:01:34.200 00:01:34.210 soldered between these two points here
00:01:36.149 00:01:36.159 we have to remember that there's more
00:01:37.710 00:01:37.720 within one element on the PCB in fact
00:01:40.499 00:01:40.509 there are more than a hundred therefore
00:01:43.350 00:01:43.360 the capacitance between these two points
00:01:45.240 00:01:45.250 would be really hard to calculate this
00:01:47.700 00:01:47.710 is why even theoretically based on the
00:01:50.310 00:01:50.320 knowledge of school physics is not
00:01:52.010 00:01:52.020 possible to measure the capacitance of
00:01:54.420 00:01:54.430 an element without desoldering it from a
00:01:56.940 00:01:56.950 PCB enough with theory though let's move
00:02:00.630 00:02:00.640 on to the real world
00:02:02.910 00:02:02.920 we will conduct an Eevee experiment with
00:02:05.770 00:02:05.780 a number of different measurements on
00:02:07.209 00:02:07.219 this PCB as you can see it has many
00:02:10.150 00:02:10.160 different components electrolytic
00:02:12.460 00:02:12.470 capacitors SMD capacitors inductors
00:02:16.500 00:02:16.510 resistors microchips light-emitting
00:02:19.000 00:02:19.010 diodes it has the works we will conduct
00:02:22.180 00:02:22.190 our measurements in different phases I
00:02:24.539 00:02:24.549 have already completed the first one by
00:02:27.039 00:02:27.049 writing down all of the nominal
00:02:28.390 00:02:28.400 capacitance values in the points where
00:02:30.400 00:02:30.410 measurements will be taken there's one
00:02:33.009 00:02:33.019 exception
00:02:34.020 00:02:34.030 there is no capacitor in point five as
00:02:37.240 00:02:37.250 it has been previously removed just for
00:02:40.360 00:02:40.370 kicks we will measure the capacitance in
00:02:42.190 00:02:42.200 this point as well in Phase two we will
00:02:46.360 00:02:46.370 measure the capacitance of those points
00:02:47.920 00:02:47.930 without desoldering the capacitors in
00:02:49.539 00:02:49.549 Phase three I will decide are all
00:02:51.610 00:02:51.620 capacitors measure their capacitance as
00:02:53.800 00:02:53.810 usual and record the values we will then
00:02:56.349 00:02:56.359 compare them to the original values and
00:02:58.119 00:02:58.129 find a result let's begin we'll turn on
00:03:01.059 00:03:01.069 the multimeter as you can see I chose a
00:03:04.360 00:03:04.370 unity UT 139 C because it measures
00:03:08.080 00:03:08.090 capacitance very well we also have
00:03:10.390 00:03:10.400 another video about this so let's
00:03:13.629 00:03:13.639 measure point 1 the capacitance is
00:03:23.970 00:03:23.980 one hundred microfarads
00:03:27.480 00:03:27.490 it's supposed to be 47 we already see an
00:03:31.360 00:03:31.370 inconsistency point - let me try again
00:03:45.510 00:03:45.520 somewhere close to 164 164 microfarads
00:03:54.750 00:03:54.760 obviously its capacitance is
00:03:56.740 00:03:56.750 significantly different from the value
00:03:58.270 00:03:58.280 printed on the capacitor in point three
00:04:04.390 00:04:04.400 we should have four hundred and seventy
00:04:05.890 00:04:05.900 micro for ads however we get almost one
00:04:13.210 00:04:13.220 militar at this is two times as high
00:04:18.330 00:04:18.340 let's record this the capacitance should
00:04:25.450 00:04:25.460 be 47 in point four
00:04:33.090 00:04:33.100 and it's about 164 microphones
00:04:45.720 00:04:45.730 in point five right here there's no
00:04:48.990 00:04:49.000 capacitor but for the accuracy of the
00:04:51.810 00:04:51.820 experiment let's measure it as well what
00:05:00.270 00:05:00.280 can I say it looks like we have an
00:05:02.550 00:05:02.560 invisible capacitor on the PCB with a
00:05:04.950 00:05:04.960 capacitance of 58 micro farad's
00:05:07.860 00:05:07.870 we should patent this technology I will
00:05:16.680 00:05:16.690 also record zero in this slot as there
00:05:19.440 00:05:19.450 is no capacitor here lastly point six we
00:05:24.120 00:05:24.130 should have 100 microfarads let's see
00:05:27.210 00:05:27.220 what we get
00:05:36.610 00:05:36.620 sixty-six microphones this is the most
00:05:47.810 00:05:47.820 accurate measurement so far with a
00:05:49.790 00:05:49.800 thirty five percent error as you can see
00:05:53.030 00:05:53.040 from this first step if we measure
00:05:54.530 00:05:54.540 capacitance without desoldering
00:05:56.000 00:05:56.010 capacitors from the PCB there is a big
00:05:58.850 00:05:58.860 difference between the nominal or stated
00:06:01.250 00:06:01.260 values and the measured values we will
00:06:04.340 00:06:04.350 now disorder and measure them in a more
00:06:06.290 00:06:06.300 correct way it is possible that some of
00:06:09.230 00:06:09.240 the capacitors capacitance has changed
00:06:11.480 00:06:11.490 over time
00:06:41.380 00:06:41.390 capacitor number three number four there
00:07:03.590 00:07:03.600 is no capacitor number five and number
00:07:08.780 00:07:08.790 six this soldering iron tip is not very
00:07:12.110 00:07:12.120 convenient for tasks like these a bigger
00:07:15.110 00:07:15.120 one would have been better
00:07:31.490 00:07:31.500 so I have D soldered the capacitors now
00:07:35.670 00:07:35.680 let's measure their actual capacitance
00:07:40.820 00:07:40.830 it looks like our multimeter has
00:07:43.080 00:07:43.090 automatically switched off we will use a
00:07:47.640 00:07:47.650 different test lead this time as the
00:07:49.670 00:07:49.680 standard one is not convenient for this
00:07:52.110 00:07:52.120 type of measurement that's because the
00:07:54.840 00:07:54.850 capacitor leads are gone
00:08:13.720 00:08:13.730 as you can see this one has a
00:08:17.200 00:08:17.210 capacitance of 67 microphones
00:08:49.220 00:08:49.230 and this one has 46 microphones the same
00:08:55.590 00:08:55.600 as the value printed on the capacitor
00:09:07.300 00:09:07.310 capacitor number three its capacitance
00:09:10.340 00:09:10.350 should be 470 micro farad's
00:09:25.930 00:09:25.940 445
00:10:02.819 00:10:02.829 here it's 49 microphones and in our
00:10:11.409 00:10:11.419 first or in this case our last capacitor
00:10:14.199 00:10:14.209 with a printed value of 47 microphones
00:10:17.049 00:10:17.059 and a measured value on the PCB of
00:10:19.239 00:10:19.249 around 100 about 48 microphones
00:10:40.570 00:10:40.580 the results speak for themselves the
00:10:43.700 00:10:43.710 capacitance values are incorrect in
00:10:45.320 00:10:45.330 every point except the last one but this
00:10:48.170 00:10:48.180 is an exception to the rule rather than
00:10:50.090 00:10:50.100 proof here we didn't even have a
00:10:52.820 00:10:52.830 capacitor and we measured 58 microflora
00:10:55.460 00:10:55.470 ads over here we had a stated
00:10:57.830 00:10:57.840 capacitance of 47 microphones we
00:11:00.290 00:11:00.300 measured it on the PCB at 164 and it
00:11:03.770 00:11:03.780 turned out to actually be somewhere
00:11:05.480 00:11:05.490 around 46 to 47 here the measured
00:11:08.720 00:11:08.730 capacitance was almost twice as high as
00:11:10.790 00:11:10.800 the actual one the same here with 164
00:11:16.190 00:11:16.200 microphones when it should have been 49
00:11:18.700 00:11:18.710 here we measured 100 microfarads in the
00:11:21.710 00:11:21.720 PCB but it's actual capacitance is a
00:11:24.110 00:11:24.120 mere 48 microphones so as we can clearly
00:11:27.410 00:11:27.420 see the measurements that are in the
00:11:29.990 00:11:30.000 second column are not measurements at
00:11:32.120 00:11:32.130 all they are more like a lottery number
00:11:34.520 00:11:34.530 from a fortune cookie some may say that
00:11:36.920 00:11:36.930 I wasn't using a special RLC meter that
00:11:39.260 00:11:39.270 measures ESR but regular multimeter
00:11:41.360 00:11:41.370 instead first of all this multimeter
00:11:44.450 00:11:44.460 measures capacitance very accurately as
00:11:46.850 00:11:46.860 we have previously shown secondly what
00:11:50.030 00:11:50.040 is ESR it's basically a series of
00:11:53.290 00:11:53.300 resistances therefore no matter what you
00:11:56.690 00:11:56.700 use for your measurements even if it's
00:11:59.270 00:11:59.280 the best device for measuring
00:12:00.920 00:12:00.930 capacitance you cannot measure the ESR
00:12:03.620 00:12:03.630 of an individual capacitor instead you
00:12:06.440 00:12:06.450 will end up measuring an equivalent
00:12:07.850 00:12:07.860 value of the entire circuit many devices
00:12:10.910 00:12:10.920 present themselves as tools that can
00:12:12.560 00:12:12.570 measure capacitance without desoldering
00:12:14.240 00:12:14.250 the elements of a PCB most of the
00:12:17.840 00:12:17.850 descriptions written online have one
00:12:19.520 00:12:19.530 main idea a small voltage is applied to
00:12:24.440 00:12:24.450 these points in a way that supposedly
00:12:26.660 00:12:26.670 doesn't affect anything surrounding them
00:12:28.760 00:12:28.770 just this small area so this capacitor
00:12:32.450 00:12:32.460 will not be affected anymore and it will
00:12:34.520 00:12:34.530 not take part in the measurements but
00:12:36.830 00:12:36.840 that's all bogus because it's impossible
00:12:39.170 00:12:39.180 to measure this capacitor if there are a
00:12:41.810 00:12:41.820 lot of other things here on the PCB you
00:12:45.650 00:12:45.660 can measure anything else you want but
00:12:47.660 00:12:47.670 not the capacitor
00:12:49.190 00:12:49.200 actually you can measure an equivalent
00:12:52.040 00:12:52.050 capacitance but not the capacitance of
00:12:55.040 00:12:55.050 this particular capacitor by itself
00:12:57.920 00:12:57.930 therefore do not buy these devices
00:13:01.000 00:13:01.010 instead by regular quality multimeters
00:13:04.460 00:13:04.470 you don't necessarily need this one even
00:13:07.400 00:13:07.410 just make sure you buy regular measuring
00:13:09.949 00:13:09.959 equipment from good manufacturers and
00:13:11.960 00:13:11.970 measure things properly in this video I
00:13:14.990 00:13:15.000 have shown you that measuring
00:13:16.100 00:13:16.110 00:13:17.629 00:13:17.639 capacitors from a PCB is a myth please
00:13:20.750 00:13:20.760 like this video if you found it useful
00:13:22.280 00:13:22.290 and subscribe to our Channel we hope you
00:13:24.259 00:13:24.269 have a great day and take correct
00:13:25.759 00:13:25.769 measurements
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