Cracked SMD inductor damage assessment - Page 1
Forum section: electronics / repair

author: unturned3
author_rank: Contributor
timestamp: September 30, 2022, 08:03:48 am
content: I recently purchased a Wifi module and I noticed a cracked SMD inductor on the back. The seller assured me that this is a common surface crack, and it would be fine since the inductor's ferromagnetic core is not damaged. However, that sounds somewhat dodgy to me... not sure what do you all think?

author: wraper
author_rank: Unknown
timestamp: September 30, 2022, 08:11:00 am
content: It IS a ferrite core that is cracked. It's parameters should have changed a bit but inductor should still be functional.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 30, 2022, 08:34:02 am
content: It is not just cracks but some small parts missing. This would reduce the inductance somewhat, but not very much (e.g. < 10% range). So Chances are very high it is still functional with no real negative effect.

author: thinkfat
author_rank: Unknown
timestamp: September 30, 2022, 11:11:49 am
content: Quote from: Kleinstein on September 30, 2022, 08:34:02 amUnless of course the stem of the core is also cracked, but that's not visible from up top. You could try wiggling the inductor, see if it budges.

author: coppercone2
author_rank: Super Contributor
timestamp: September 30, 2022, 07:56:06 pm
content: if the top is just chipped off in the corner it should be OK unless the circuit was way too optimized or barely functioning. The inductor tollerance is wide usually, so you have a few % change.. but chances are its in spec, since it might be +-30% part.

author: thm_w
author_rank: Super Contributor
timestamp: September 30, 2022, 09:09:38 pm
content: Quote from: Kleinstein on September 30, 2022, 08:34:02 amTried this out to verify, measurements taken in circuit, cracked off the top:- Original: 4.46uH Rs 89mR- 25% crack: 3.85uH- 60% crack: 3.15uHOPs looks something like 20% of the top has been cracked off, so probably around the 10-15% reduction in inductance range.Quote from: coppercone2 on September 30, 2022, 07:56:06 pm-15 to -20% is the most common tolerance option. -30% does exist though.

author: coppercone2
author_rank: Super Contributor
timestamp: September 30, 2022, 10:47:54 pm
content: i stand corrected, its dodgy. Some how I missed that its WiFi. You don't want messed up inductors near a radio.

author: wraper
author_rank: Unknown
timestamp: October 01, 2022, 06:42:12 am
content: Quote from: coppercone2 on September 30, 2022, 10:47:54 pmAt its frequency of operation it's pretty much irrelevant to WIFI, so only concern is about buck converter working properly.

author: thinkfat
author_rank: Unknown
timestamp: October 02, 2022, 10:26:02 am
content: Quote from: wraper on October 01, 2022, 06:42:12 amIf it even is part of buck regulator. There is suspiciously nothing nearby that would scream "voltage regulator". Could be on the bottom PCB side, of course, but the whole group could as well be part of a filter for a voltage rail.

author: unturned3
author_rank: Contributor
timestamp: October 05, 2022, 07:55:14 pm
content: Thanks for the replies everyone! I'll test this module once I get access to a Linux machine (sadly the drivers aren't available on MacOS 12.4) and will report back if I notice any oddities.

author: kjr18
author_rank: Regular Contributor
timestamp: October 11, 2022, 11:29:32 am
content: Once I took apart my old Kingston SSD, and found that one of inductors is missing piece of it's core. Missing piece was nowhere to be found inside case. Disk works just fine.

author: coppercone2
author_rank: Super Contributor
timestamp: October 13, 2022, 06:06:29 pm
content: well when this happened on a pickit3 for me it would act up, but that was on a regulator

author: ogden
author_rank: Super Contributor
timestamp: October 13, 2022, 06:28:28 pm
content: L1 seems to form LC filter together with C8, GND referenced. As C8 seems to have quite a capacitance, I would not bother about chipped -off inductor. Most likely it is power input or output and loss of inductance here does not matter much.

author: unturned3
author_rank: Contributor
timestamp: November 07, 2022, 02:36:21 pm
content: Just verified the WiFi board on a Linux machine; it does indeed work. Thanks again everyone!