Help identifying inductor - Page 1
Forum section: electronics / repair

author: Junkie
author_rank: Newbie
timestamp: November 21, 2014, 10:29:04 pm
content: HiI am looking at repairing the pcb shown in the photo, an inductor has overheated and detached from the board.I have the faulty inductor and it is marked the same as the inductor that I have circled on the attached photo.Could anyone tell me, would this be a 37 micro henry inductor or 3.7 or something else??ThanksJunkie

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 22, 2014, 01:26:47 am
content: I'd want to measure it. "37" is too ambiguous.Tim

author: Raff
author_rank: Regular Contributor
timestamp: November 22, 2014, 05:58:32 am
content: I agree, measure it if you can as 37uH doesn't sound like a standard value anyway.

author: Junkie
author_rank: Newbie
timestamp: November 22, 2014, 09:42:41 am
content: Unfortunately I currently have no way of measuring inductance, does anyone have any experience of cheap lcr meters off ebay? Would one of these be any good?Junkie

author: Seekonk
author_rank: Super Contributor
timestamp: November 22, 2014, 10:05:09 am
content: That looks like a filtering inductor and it wouldn't be critical. The bigger inductor would be critical because it is part of the regulator circuit. Since the little one over heated due to high current, there is likely a short in the circuit it powered. I would start by making a resistance measurement from that contact to common. It is doubtful replacing just that inductor will solve the problem.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 22, 2014, 10:08:12 am
content: looking at the data sheet, it appears to be on the input to the regulator, so as mentioned, its not really critical...but as also mentioned, you need to figure out why it failed

author: Raff
author_rank: Regular Contributor
timestamp: November 23, 2014, 07:04:00 am
content: I've got one of those Mega328 based "fish88" component testers, it measures inductors pretty well, especially for something that cost $25 including postageI bought from this eBay store, although the price has risen a little.http://www.ebay.com.au/itm/M328-ESR-Meter-led-Transistor-Tester-Diode-Triode-Capacitance-MOS-PNP-NPN-L-C-R-/311031023109?pt=AU_B_I_Electrical_Test_Equipment&hash=item486ae4c605I also bought one from here for a mate, when he saw mine he had to have one

author: Richard Head
author_rank: Frequent Contributor
timestamp: November 23, 2014, 09:17:14 am
content: It wouldn't surprise me if you soldered it back in place and the card worked. It may have overheated and unsoldered itself due to excessive load current.

author: Junkie
author_rank: Newbie
timestamp: November 24, 2014, 12:25:42 pm
content: Cheers for the advice, it appears the inductor was indeed just for filtering and there was a (partial) short in another board that the boost circuit was powering.....The circuit being powered is a ccfl invertor for a 4"tft display, there is no dead short but the circuit is drawing excessive current, I desoldered the fuse shown in the photo below and the circuit now powers up ok, now just need to fault find the inverter board.... What's the chances it could be a leaky capacitor ( they all physically look ok)??Junkie

author: EMUD
author_rank: Regular Contributor
timestamp: November 24, 2014, 04:25:56 pm
content: Hi,you don´t need a inductance meter to measure it. What you need is a frequency generator (up to 100KHz is ok)and an oscilloscope. Take the inductor in series with a capacitor ( use 10nF or 100nF) between the generator and the osc. If you have a digital multimeter wich covers the frequency range up to 100KHz you may use it instead of the osci. Shorten the osci input with a 1K resistor. Now increase the frequency of the generator, you will find a maximum amplitude on your scope or dvm. Note this frequency. Now you are able to calculate the inductance (Thomson formula). If you have problems with the formula look for downloading "mini Ringkern-Rechner 1.2", its freeware und you can switch its screen to english.But i think too, that soldering the inductor again will repair your supply. These are heavy components and are sometimes soldered bad.EMUD