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While working on a tablet motherboard I encountered this creature:

enter image description here

Its resistance is 0 ohm and it's very dark, so it seems to be a 0 ohm SMD resistor. But I thought that 0 ohm resistors are marked with "0".

The dimensions are 1.97x1.17x0.8mm.

Is it a 0 ohm resistor or a shorted capacitor? As far as I know, resistors do not short.

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    \$\begingroup\$ If you are sure it is not a self or a ferrite then it is a a strap/zero ohm resitor. From the photo I'm 80% sure it is one. \$\endgroup\$
    – francois P
    Oct 25 '21 at 14:42
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    \$\begingroup\$ 0 ohm resistors are usually marked with a zero (or a single black line in case of through-hole). I would also assume that this is a ferrite. \$\endgroup\$
    – Lundin
    Oct 25 '21 at 14:47
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    \$\begingroup\$ It's a ferrite bead \$\endgroup\$
    – Kyle B
    Oct 25 '21 at 15:18
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    \$\begingroup\$ You can get a cheap "transistor tester kit" from the likes of eBay which will also identify and measure LCR components for you. \$\endgroup\$ Oct 25 '21 at 15:51
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    \$\begingroup\$ @Lundin At least in 0805 chips they usually are, on 0603 and especially on a 0402 it's not a given anymore. The text on 0402 would be very very small so often they're blank. \$\endgroup\$
    – Barleyman
    Oct 25 '21 at 17:18
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It's hard to tell definitely what it is without measuring its complex impedance at several frequencies. If you do any sort of component-level repair, having a network analyzer with a component test fixture would be helpful - even a cheap one would be better than nothing. That way you could definitely identify such passive components, and ensure that the replacements have similar performance. Barring that, an RLC bridge or meter would be the next best thing, since you'll be able to take measurements at several frequencies (e.g. 100Hz, 1kHz, 10kHz, 100kHz). To an ohm meter, resistors and inductors are indistinguishable, since at DC an inductor is just a resistor.

Judging by the surface texture, and by how 0-ohm jumpers typically look, I'd say what you have is not a 0-ohm jumper, but an inductor of some kind. Further, it's unknown whether the ceramic core material is meant to have highly dissipative properties like an EMI suppression bead would, or not - like in a general-purpose inductor.

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That cuticle shape of the pads is characteristic of ferrite beads, for some reason. As is the black sides of the part.

enter image description here

Resistors typically expose the alumina substrate on the sides:

enter image description here

It's hard to distinguish electrically if you don't have proper equipment, certainly the cheapie ATMega328p boards will not do it. It's also very difficult with cheap low frequency LCR bridges- the inductance at low frequencies is typically only a few microhenries.

It's possible to use a spectrum analyzer with tracking generator, which will allow you to sweep over the 100MHz range where ferrite beads are typically specified. That won't show you the phase information as a real impedance analyzer would but at least it will verify the large-print datasheet specification (such as 600\$\Omega\$ @ 100MHz).

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  • \$\begingroup\$ Thanks. You always write informative answers. Do you know why the inductance is a function of frequency? Is it because the magnetic permeability of the material is a function of frequency or there is some more important reason? \$\endgroup\$
    – apadana
    Oct 27 '21 at 1:26
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    \$\begingroup\$ To a first approximation you can model the bead as R/C/L all in parallel. At low frequencies the L dominates the impedance, it's resisitive in the middle range and capacitive at really high frequencies. See this application note for more info. SPICE models can get quite complex for real ferrite beads. \$\endgroup\$ Oct 27 '21 at 5:47
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It's likely a 0805 ferrite bead. https://en.wikipedia.org/wiki/Ferrite_bead

For example: https://www.digikey.com/en/products/detail/laird-signal-integrity-products/HI0805Q310R-10/806633

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