Yes, I'm a noob. I am trying, please be nice.

I am trying to test the parts on an LED driver that's gone bad. Mainly because I actually NEED the thing to work, but also so I can learn how to do this sort of thing.

Mains in to a fuse (which is fine), then to this film capacitor. Multimeter on CAP setting gives me 125.5 nanofarads. (Why the meter doesn't auto-adjust to uF is yet another mystery, but that's another question.)

I can use the label info from the SIDE to find this document: https://www.pcb-3d.com/wordpress/wp-content/uploads/CAPRR_EPCOS_B32921-B32926_SERIES.pdf

Below the legible printed info on the side there are only the 'reversed LR' symbols and the 'EN over EC' symbol.

On page 3 you'll find the match for the series, but showing 6 uF variations. None of the six values make sense to me as a match for what I measured with the multimeter.

I know that I am meant to use the info from the TOP label to figure out the proper farad value, but for the life of me I can't figure out how to do that.

Some of it's obvious - 305V A/C. But the rest of the info doesn't seem to match the info in that doc? I am really confused by this.

If you can just tell me the value, great. That's enough to let me know if it's the .10 uF version and my .1255 uF actual measure is close - or if my actual measure is way off what it is supposed to be.

But if you can also explain how I'm meant to translate the label that'd be way better.

Phrased as proper questions:

What capacitance is the pictured capacitor?


How does one use the text on the label to determine the capacitance?

enter image description hereCapTop

  • \$\begingroup\$ "B1-U1" almost matches the top-right example. 0.1255uF is a bit out of spec for "M" though. \$\endgroup\$ – Ignacio Vazquez-Abrams Jun 7 '18 at 0:02
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    \$\begingroup\$ Did you desolder it before measuring its capacitance? You can't trust capacitance measurements made in-circuit, generally. \$\endgroup\$ – Hearth Jun 7 '18 at 0:16
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    \$\begingroup\$ @Nixt You don't know what you're measuring if you leave it in-circuit. There could be all kinds of junk in parallel with the capacitor that could mess up your reading. \$\endgroup\$ – Hearth Jun 7 '18 at 2:23
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    \$\begingroup\$ @Nixt. You will get nowhere unless you pull out parts, even just one lead, and check them independently. I do NOT believe an X2 capacitor has failed open. It would not stop the circuit from working if it did fail. \$\endgroup\$ – user105652 Jun 7 '18 at 2:50
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    \$\begingroup\$ INFO: Have a local uni student looking at it. He just texted me to tell me it's all working to just past the bridge rectifier, which means this cap is not faulty. Still want to know how to read/identify it though, please? \$\endgroup\$ – 111936 Jun 7 '18 at 4:25

That is an X-type safety capacitor).

Printed on the side:

MKP/SH: denotes polypropylene film dielectric, self-healing

B32921: denotes the case size; this case size is typically rated 305VAC.

40/105/56: Climatic Code from IEC 60068-1, interpreted as follows, obtained from here

CLIMATIC CATEGORY The climatic category indicates the climatic conditions which the capacitor may be operated.
According to IEC 60068-1 the climatic category is expressed by a three group coding e.g. 55/100/56. - The first group indicates the lower category temperature (- 55 °C). - The second group the upper category temperature (+ 100 °C). - The third group indicates th e number of days (56) which the capacitor can withstand within specified limits if exposed to a relative humidity of 95 % and a temperature of + 40 °C.

I suspect if you can view the rest of the component markings you will find the capacitance, tolerance, and probably the voltage.

  • \$\begingroup\$ As in posted question:"If you can just tell me the value, great. ... But if you can also explain how I'm meant to translate the label that'd be way better." I already understand that the other markings will somehow code the capacitance - this is exactly what I seek help with. \$\endgroup\$ – 111936 Jun 7 '18 at 8:27
  • \$\begingroup\$ Just thinking about how I didn't use a question mark in the original to clearly indicate where the dual-part question is. I will edit the question to include fully formed questions with question marks. \$\endgroup\$ – 111936 Jun 7 '18 at 8:50

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