# Component identification (SMD) - Beelink X55 Ultimate

Recently my NUC has decided to release some magic smoke. I found two problematic components in it. F1 fuse, which failed (?) to protect the board and U10 which has manifested a nice eruption point.

U10 seems to be marked as B3103 J1306E (or B8103 J1306E) but I cannot find a replacement component. Contacting the manufacturer has so far not yielded any results. Anyone have any ideas what it could be?

Any help on identifying the fuse would be appreciated, though I assume the problem is with U10 which malfunctioned and not the fuse?

Late edit:

Well, I finally fixed the issue. As was correctly stated by @ChrisStratton in a comment this was not the original failure. The short from 12V to ground persisted, but the replaced mosfet did not blow as I connected the device to a current limited PSU, limited to 12V@0.15A, it did get toasty warm. I finally tracked it down to a faulty ceramic capacitor (or perhaps it was promoted to a 0R bridge resistor!).

Removing that sucker fixed everything up and now it is booting back up! Seems it purpose was just a capacitor bank, but still need to replace it, for now the device runs without it. As for the value, no idea, I'll probably just add a beefy cap (1uF).

The bloody fuse still works, YOU HAD ONE JOB TO DO FUSE!

Was fun to learn to do to SMD rework, always wanted to do it but never found an excuse :) Luckily the board and components were small enough not to require PCB heater...

For posteriorities sake, in hopes it helps someone else, the faulty capacitor was found between Q168 and Q171 as shown in the bellow image (capacitor is already removed).

• A likely guess would be a MOSFET, especially if on removal with a hot air tool you see that multiple pins are tied together. That said, this is probably not the original failure. Likely even if you found and installed a replacement, that would immediately blow as well as the original fault would remain elsewhere. Systems like this aren't readily repairable without an understanding of what is going on in the circuit, and absent that repair questions are generally ruled off topic here. Aug 27 '19 at 13:41
• Not asking for assistance in repair or any such thing, only for help in identification of component. It may be a MOSFET, thank you. Will have a peak under the component.
– Honf
Aug 27 '19 at 14:05

As suggested by Chris Stratton in a comment, the SMD code B3103 and the DFN package seen in the photo, matches a MOSFET:

Rectron RM35P30DN P-Channel Enhancement Mode Power MOSFET - datasheet link

From page 6 of the datasheet:

• Yes, think should fit the bill! Wonderful, a big thanks to everyone. I am left with one question, where can I lookup the Device marking to the Device name in the future? Searching by the Device marking gave me zero results on google, mauser and digikey, but the device name however gives plenty of results.
– Honf
Aug 27 '19 at 21:27
• Device markings are hard to find, you have to search google, and as many manufacturers as you can, there is no one central place to find this information Aug 27 '19 at 22:11
• @Honf - Hi, "where can I lookup the Device marking to the Device name in the future?" There is no guarantee of success, as there is no central database of every marking-to-name mapping. Voltage Spike kindly wrote this (self-answered) question, which gives useful resources and explains some identification techniques. Good "Google-fu" also helps, as does experience e.g. that package type is quite common for power MOSFETs. Aug 27 '19 at 22:11

It looks like its a Pchannel mosfet FETek FKBB3103
Data sheet here:
http://www.fetek.com.tw/data/FKBB3103.pdf

• Thank you, this and the one provided by SamGibson seem to fit the bill.
– Honf
Aug 27 '19 at 21:28
• It looks like this is a knock off of the other one. Aug 27 '19 at 21:45
• Well, at least they used the correct schematic :) The rectron uses a n-channel schematic but its a p-channel (unless I am misinterpreting).
– Honf
Aug 27 '19 at 21:53

The fuse looks typical of the ones from Little fuse. If you get the package size you should be able to find it with its case marking easy enough. I can't quite make out the size from photo. https://www.littelfuse.com/products/fuses/surface-mount-fuses/thin-film-chip-fuses.aspx