Help buying an SMD coil for a laptop replacement.. - Page 1
Forum section: electronics / repair

author: zdelarosa00
author_rank: Regular Contributor
timestamp: August 16, 2019, 06:44:13 pm
content: Hello, so a couple days ago I turn on my laptop and on the loading OEM logo boot up it glitches the screen a bit and proceeds to turn off (all this a couple seconds after the initial button press), nothing was messed around with beforehand, and then I proceed to not turn it on again and open it up, so after a close inspection I found a pair of caps that were burned, so after not having much luck on finding the original motherboard to replace, I luckily find the correct schematic and found the corresponding burnt part, it is actually a coil instead of a capacitor, but in the attached pictures the parts just next to it also show a bit of damage, so maybe I will replace those too… My pictures show a before and after I clean with Isop Alcohol so after the damage to the coil is not so obvious, I attach both.My question is, what does this mean on the schematic? The part is listed as PL9, and it’s value is “80/5A”, my first thought was 80uH, 5A, but that’s not very plausible. And the mouser electronics (I live in Mexico) page doesn’t list SMD coil values as high as that.How can I figure the value of the part so I can replace it?I am searching the part in this site:https://www.mouser.mx/Passive-Components/Inductors-Chokes-Coils/Fixed-Inductors/_/N-wpcz

author: benj38
author_rank: Frequent Contributor
timestamp: August 16, 2019, 07:52:14 pm
content: It may be that 80 stands for 8 with zero zeroes, i.e., 8uH. This would be consistent with the fact that 8UH/5Amp coils of this size (as far as I can guess it from the images) are not uncommon.Note that the schematic shows PL10, PL15 and PL16 all being equal to PL9.Thus, measuring the (out-of-circuit) inductance of these other coils will allow you to deduce if the conjecture above is correct.

author: pigrew
author_rank: Frequent Contributor
timestamp: August 16, 2019, 10:05:48 pm
content: It looks like the inductor is used as a EMI filter ("pi" filter with the two adjacent capacitors) on the battery connector to filter the charger's switching converter noise. The value shouldn't be so critical, and the laptop should even work with you just bridging it with a bit of wire.It is connected to a BQ23748 charger which doesn't seem to have a publicly available datasheet. However, the BQ23745 suggests a 4.7uF LC filter. Having two in parallel, means that 8.0 uH is about what they suggest for this different part.If one of PL9 and PL10 is fried, then probably both are bad, preventing the laptop from running off of battery properly. If the battery is removed and the AC adapter connected, does it work properly?If you remove PC206, then you could measure the value of the two parallel inductors on the board which are next to the AC adapter input. If your LCR meter has a guard, you could also connect the "Guard" to your board's ground and measure the inductance across the inductors without removing any components (at low-ish frequencies), if the guard terminal is able to overpower the capacitors.

author: zdelarosa00
author_rank: Regular Contributor
timestamp: August 16, 2019, 10:34:07 pm
content: Indeed 8uH sounds about what should be the value, I will try and remove the apparently good ones to check. But the thing is, 5A is the correct nominal current? Because my provider doesn't show that type of SMD package neither with 8uH or with 5A rating and if I scale down to search 8nH it shows only this coil:https://www.mouser.mx/ProductDetail/TE-Connectivity/36401E8N0ATDF?qs=sGAEpiMZZMsg%252By3WlYCkU3XRdJoqtyIJ6aM%252B8FnTgf8%3DI attach the results of the 8uH/5A search results.

author: DaJMasta
author_rank: Super Contributor
timestamp: August 16, 2019, 10:58:04 pm
content: Could it be an 80 ohm impedance 5A rated ferrite bead?

author: zdelarosa00
author_rank: Regular Contributor
timestamp: August 16, 2019, 11:39:36 pm
content: That's very possible, but what about the diagram showing it is a coil? I've found some with close values to 80ohms and 5A but not exactly.They're indeed very similar though:https://www.mouser.mx/ProductDetail/Murata-Electronics/BLM18KG300TZ1D?qs=sGAEpiMZZMt1hubY80%2Fs8I8WoiTpYN3QX0r%252Bq7NNXrufoLQPZuaDow%3D%3D

author: amyk
author_rank: Super Contributor
timestamp: August 17, 2019, 12:14:35 am
content: It's definitely an inductor, as the PL designator (P for power, L for inductor), symbol, and position in the circuity suggests. An 80 ohm resistor in a laptop power circuit that passes several amps would not make sense, but an 80milliohmferrite bead does.Observe that lower on that page of the schematic there is an actual inductor marked with 4.7uH/5.5A, but PL9 and PL10 are not marked the same way, which is why I suspect it's a ferrite bead.

author: DaJMasta
author_rank: Super Contributor
timestamp: August 17, 2019, 12:30:57 am
content: Quote from: amyk on August 17, 2019, 12:14:35 amFerrite beads are often specified by Ohms of impedance (not resistance) at a specific frequency (100Mhz, commonly), so their DCR is much lower, on the order of tens of milliohms if it's gotta pass 5A. You could have a 100+ ohm ferrite bead of that size with low DCR, they are sometimes indicated by L on a schematic/silkscreen, and they do sometimes just use an inductor symbol, since that is basically what they are... I haven't personally seen them labeled PL, though, and I haven't seen any in the tan packages circled, but I think that sort of current rating and package size about match with the pair of black parts in the circle.Really, if you want an inductor with 5A of current rating and a uH ballpark of value..... it's going to have to be larger than that. Typical power inductors in that 4.7uH range rated for 5A are going to be 6x or more the volume even if the profile is small. Since ferrite beads are effectively a single turn through a ferrite material, their inductance is much lower but their package size can be MUCH smaller for the same current rating.For example, this one:https://www.digikey.com/product-detail/en/laird-signal-integrity-products/HI0805R800R-10/240-2395-2-ND/806634And if you want to check them, their DCR should be very low and their inductance in the 10s or 100s of kHz range will still be in the nH range. It will basically appear as a dead short because the damping effects (higher inductance) of the ferrite material kick in at much higher frequencies.

author: james_s
author_rank: Super Contributor
timestamp: August 17, 2019, 12:31:31 am
content: It's worth mentioning that if those inductors fried there's a good chance that a short elsewhere caused them to burn. I would expect to find shorted semiconductors down the line, have you tested for shorts?

author: Dimebag_arsa
author_rank: Newbie
timestamp: July 06, 2020, 05:13:47 pm
content: Quote from: zdelarosa00 on August 16, 2019, 10:34:07 pmHello, did you find the correct component to solve your issue?I'm struggling knowing what kind of component PL9 is.If you could tell me the component you used to fix your computer and where you bought it (I'm from Mexico too) I'll be very grateful.