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I bought this board a while back:

photo
(source: seeedstudio.com)

http://www.seeedstudio.com/wiki/GPRS_Shield_V1.0

I mistakenly connected positive and negative instead of each other and the yellowish thing near the power select on the board (477 j / 110 m 3) fired literally and fell off. When I correct it, it works fine.

My questions are:

  1. What is that part name and use on the board? Is it some kind of fuse?

  2. Can I just replace it? Is it necessary? The board works fine without it.

  3. The firing keeps me thinking, is it safe to put it in the car? Is it possible that fires up again?

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    \$\begingroup\$ The big yellow things appear to be tantalum capacitors. They will definitely blow up if given a reverse voltage. Tantalums aren't commonly used anymore due to various issues, except they have certain performance benefits. If you see them on a recent design, it's likely they were specifically chosen for the application. If you can figure out the package size and capacitance, you should be able to order replacements on Digikey or similar distributor. You could try to operate without it but device performance may not be good. \$\endgroup\$
    – Smith
    Aug 2, 2016 at 16:05
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    \$\begingroup\$ Be aware that regardless of replacing the tantalum cap, the board may still be damaged. Even if it appears to work fine for now. \$\endgroup\$
    – marcelm
    Aug 2, 2016 at 16:15
  • \$\begingroup\$ It is probably a short circuit. But it WAS a tantalum capacitor... \$\endgroup\$
    – user16324
    Aug 2, 2016 at 18:13
  • \$\begingroup\$ @BrianDrummond If you take that stance, it probably isn't yellow anymore either :P \$\endgroup\$
    – marcelm
    Aug 3, 2016 at 7:25

2 Answers 2

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The component you're describing is a tantalum capacitor. Read more here. It works like a regular (e.g. electrolytic) cap, probably in this circuit its function is to make the power supplied to the device "cleaner", as the GPRS module may draw lots of current in short bursts, so the capacitor acts like a short-term power reservoir. The tantalum caps allow for much more capacitance per unit of volume than electrolytic ones, but they're notorious for their narrow voltage tolerances and a spectacular thermal failure mode, which you've witnessed. Basically if you abuse them they burst into flames, sometimes sending small pieces of flaming material into the air.

It's much better for the board you if you replace it with a working one.

As per the general safety question, the technology of tantalum caps is safe enough to put them in nearly all mobile phones nowadays (as phones are too small to allow for an electrolytic cap). But in the hobbyist setting there have been cases of exploding products due to poor circuit design. Most famously and Arduino GPRS or GPS Shield (the official, branded one) designs from a few years ago had a lot of exploding specimen.

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    \$\begingroup\$ This is a very nice first answer! \$\endgroup\$
    – pipe
    Aug 2, 2016 at 16:14
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    \$\begingroup\$ Note that tantalums usually have the line, dot, or other polarity indicator on their positive side, unlike almost every other cap. \$\endgroup\$
    – rdtsc
    Aug 2, 2016 at 17:19
  • \$\begingroup\$ Also, at least some tantalum caps prescribe soldering regimes not easily followed by hand soldering methods... \$\endgroup\$ Nov 12, 2018 at 20:03
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The yellow block components are tantalum bypass capacitors. The board may appear to "work fine" without them, but it will suffer from excessive noise and reduced reliability.

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    \$\begingroup\$ Especially since they're probably associated with the voltage regulator right next to them. \$\endgroup\$ Aug 2, 2016 at 16:07

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