Here's a picture of two fuses. Both are very magnetic 😀

h-a-l-9000 wrote:

Can you do a continuity check on the part, and tell to which pin of the keyboard connector it leads? It's probably a fuse.

I've seen inductors placed instead of fuses on some boards - maybe here it's the other way around.

Any component will act as a fuse from some point on. That one is beyond that point. 😀

This one is a ferrite bead. Either way it will be used as a filter and connected in series between KB and interface (same for the inductor case). You can measure the DC resistance of the other (still intact) ones with a multimeter (should be a very low value). In that case you can try to short it with a wire (or small series resistance) in order to test if the keyboard interface is still working or was taken out by whatever happened to the broken components.

h-a-l-9000 wrote:

Here's a picture of two fuses. Both are very magnetic 😀

Mmmh. Are you sure? "F" could also designate "Ferrite" or "Filter".

See:
http://www.digikey.com/product-search/en/filt … =0&pageSize=500

Have to admit that there are indeed fuses from a company called "Eaton" that look very similar:
http://www.digikey.com/product-detail/en/bel- … 16-1-ND/3516817

Other fuses in that format usually have the nominal current printed on it:
http://www.digikey.com/product-detail/en/bel- … -1037-ND/614983

If there is a small gap between the wire and the case - then I'd bet on ferrites however.

> This one is a ferrite bead.
L3 is a fuse. Check out the picture of the other mainboard.

> Mmmh. Are you sure? "F" could also designate "Ferrite" or "Filter".
The standard for schematics is L for inductor, F for fuse, R for resistor, X for crystal and so on. The manufacturer can of course decide to place something else for several reasons.

This is also a matter of experience - On the boards I've seen it was either a fuse, a ferrite bead or a wire bridge in this function. The L3 part is too slim to be a usual ferrite bead. Inside it's shaped like a resistor. And I've seen fuses like that (but in green) at the keyboard connector on other boards. On my photo the beads are in series to the data lines of the keyboard, fuses make no sence there.

h-a-l-9000 wrote:

On my photo the beads are in series to the data lines of the keyboard, fuses make no sence there.

I second this. Based on photos of identical motherboard with fuse and the charred remains on device passing 5V supply to keyboard, it was not a ferrite but a fuse.

As ferrite beads are basically just a piece of wire within a ferrite material bead, it should pass several amps without heating too much, and it has nothing that would melt like plastic.
If it had been a ferrite bead, it would be intact looking shiny as ever, and the motherboard copper traces would have been vaporized from the excess current/shortcut (maybe a broken keyboard was attached).

So even if the original design may have had a ferrite on keyboard power supply line, it made sense to manufacture it with fuse instead.
No need to change the silk screen print on hundreds of already manufactured blank PCBs waiting to be populated with components.

Success!
Checked for continuity on the sides of the fuse, there wasn't. Good sign. Desoldered it from the board and cut it open, it was indeed a fuse without any doubt. Replaced it with a 1A one I had laying around and it just worked.

Thanks a lot all of you guys for participating in this, sharing your knowledge and even researching about it, I'd had never fixed it myself!