I repair laser tag vests and on the phaser board is a strange component on what appears to be the phaserboard. See the black box on the center of the bottom, close to the left edge of the ribbon cable.

It has no reliably measurable resistance and as far as I can tell is involved in power delivery, as when it falls off (which it does often) the phaserboard no longer gets power. It has a marking on the top saying "100k" but nothing else. I would like to know what it is so I don't depend on trying to find it when it falls off and can just order new ones.

Edit: It would appear from answers that it is an inductor of some kind. During my next shift I'll try to get some closer, higher quality photos to see if we can narrow down, since I've combed through DigiKey and haven't found any matches I'm comfortable with.

Edit: Here are more pictures (I can post more if I get more reputation, sorry!):

  • \$\begingroup\$ It would help if you could provide a photo from the bottom so we can see the markings. \$\endgroup\$ – SDsolar Aug 25 '17 at 2:06
  • \$\begingroup\$ there's no access to the bottom thanks to the LCD panel. \$\endgroup\$ – Bakna Aug 25 '17 at 2:07
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    \$\begingroup\$ To measure inductance you can search for "LCR meter" \$\endgroup\$ – user253751 Aug 25 '17 at 7:04
  • \$\begingroup\$ That is a much better picture. It does indeed clearly say 100K on it. But you never know about Chinese parts. I just ordered a resistor assortment (of 10-packs) and they have some very odd markings on them. Generally I get the gist but in the end have to measure to make sure I have the right ones before I use them. If this were mine I would dab some silicone on it just to make sure it doesn't get lost. \$\endgroup\$ – SDsolar Aug 31 '17 at 1:25

Based on size, shape and marking, I agree with others that it is an inductor.

Is that a partially hidden marking of "L1" on the PCB in your photos, at the end of this component near the ribbon cable? If so, the designation of "L" is confirmation of this component being an inductor.

To be sure of its inductance (although that isn't the only part of its specification which might be important, especially if it is part of a switching power converter) then you need to remove and measure it using a suitable meter.

Again, based on its size, I respectfully disagree with other answers in the likely interpretation of the "100K" marking. I can find several sources which back-up my usual interpretation, which is that the units for reasonable size power inductors like this, are in µH with the "K" suffix being a tolerance value of +/- 10%.

(Values on much smaller inductors can be in nH - but this inductor is too large for that to apply IMHO.)

Therefore I expect its likely value is 10 µH

The marking breaks down as follows:

  • 100 = 10 (value) with a multiplier of 0 (i.e. no additional multiplier)
  • K = tolerance of +/- 10%

Here are some sources which confirm that interpretation:

Randomly chosen manufacturer's inductor datasheet showing 100K = 10 µH +/- 10%

Talking Electronics page about inductors, explaining that 100 = 10 µH

How To Wiki showing that 101K = 100 µH +/- 10% (so 100 would be 10 µH +/- 10%)

Another random manufacturer's datasheet, Würth this time, showing that a marking of 220 would be 22 µH (so 100 would be 10 µH)

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    \$\begingroup\$ Thanks! This appears to be correct. Will confirm when the inductors I ordered arrive and I can test them on a broken board. \$\endgroup\$ – Bakna Aug 26 '17 at 7:37
  • \$\begingroup\$ @Bakna - You're welcome. :-) As I said, some other parameters may also be important for any replacement inductor e.g. current-related ratings. If I was going to try to find a replacement for that inductor, I would reverse-engineer that power regulator circuit including identifying U3, and also try to get an idea of the load on that power rail. Also scope traces collected on a working board (with original inductor) can be compared with scope traces after a replacement inductor is installed. Finally, perhaps it's worth considering proactively supporting that inductor, if it tends to "fall off"? \$\endgroup\$ – SamGibson Aug 26 '17 at 7:44
  • \$\begingroup\$ The current plan is to patch-job with guess work and try to get the actual information from the manufacturer later on down the road. \$\endgroup\$ – Bakna Aug 26 '17 at 7:46

Inductor (hence the "L" designator), 100kuH, i.e. 100mH. Part of a power regulator no doubt, with U3 being the controller and switch.


It can't be a resister, and can't actually be marked 100k

enter image description here

I would surmise that it is a small inductor of some kind - 4 attachment points.

So if you think it might fall off the board, then I suggest you go proactive and solder it now, for reinforcement, while it is still attached.

Also, maybe mark it for orientation in case it does fall off.

  • \$\begingroup\$ Problem is, half a dozen already have and I'm capable of soldering surface mount components so I need to be able to identify it so I'm not forced to replace the whole board (which is extremely costly). \$\endgroup\$ – Bakna Aug 25 '17 at 5:40
  • \$\begingroup\$ If this were mine I would dab some silicone glue on it, then. \$\endgroup\$ – SDsolar Aug 31 '17 at 1:26

Awfully small for 0.1 H. Plus, that's a pretty large value for a switching power supply component. My vote is 10 nH, which, similar to capacitor codes, is noted as 100: the number of nH (10) followed by the number of zeros (0). K indicates 10% tolerance. A datasheet is here:



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