Unbearable coil whine on Lenovo Mini PC - Page 1
Forum section: electronics / repair

author: canadaboy25
author_rank: Regular Contributor
timestamp: March 15, 2025, 03:51:42 am
content: Hi all, I have a Lenovo mini desktop PC that has an unbearable coil whine. The frequency changes depending on CPU load. I can tell when a program has started/stopped from the other side of the room just by the coil whine. The noise is exactly the same whether I power the PC from the original AC-DC adapter, or from my bench power supply.I took the board out of the case and powered it up on the bench. I used a piece of blue tac to cover up each inductor to see if I could isolate which one was making the noise. I was not able to isolate the noise with this method. There are several inductors buried under the CPU heatsink that I was not able to cover with the blue tac. I believe it is one of the two inductors circled in the picture that is making the noise. I determined this just by ear, which is incredibly difficult with this high of a frequency as it just sounds like the noise is coming from all around you. Checking with the scope, the waveforms on these inductors do change with changes in the noise. It also makes sense that it would be one of these inductors as I assume they are for the Vcore regulation which would have a changing load based on CPU load.The markings on the inductors are "R30 1352". So a 300nH inductor and I am guessing 1352 is just a date code. I assumed inductors in these black box type packages were potted. If so, shouldn't this prevent the excessive whine?Is there any better way to pinpoint which component is causing the whine? And more importantly, is there anything I can do about it? I would think I could replace the inductors and hope that the construction is different hopefully eliminating the whine? This PC is a very handy little machine, but is just unbearable to use with the noise.Any advice is appreciated.

author: wraper
author_rank: Unknown
timestamp: March 15, 2025, 03:56:20 am
content: 95% chance it's MLCC singing and has nothing to to with coils. This board seems to lack any bulk capacitance other than MLCC before buck converters. You could try adding some polymer capacitors in parallel to MLCC. Or replace them with SMT aluminum polymer.

author: canadaboy25
author_rank: Regular Contributor
timestamp: March 15, 2025, 04:01:15 am
content: Quote from: wraper on March 15, 2025, 03:56:20 amI suspected that as well and covered every cap I could access with the blue tac. I would have thought that should at least dampen the noise if I got the right one covered.In the case of it being caps, is it generally just one offending cap, or all the caps on a particular rail making noise? If the latter, that would likely be the reason it is so hard to pinpoint.

author: Zoli
author_rank: Frequent Contributor
timestamp: March 15, 2025, 05:55:35 am
content: One of the possible reasons can be a speckle of dust between the culprit and PCB. Typical solution would be to flood under the part with conformal coating.

author: benj38
author_rank: Frequent Contributor
timestamp: March 15, 2025, 11:44:24 am
content: Use the old auto-mechanics' trick of holding the handle of a screwdriver to your ear and placing the blade of the screwdriver to the part for a make-shift stethoscope. It works very well.Be careful not to short anything with the screwdriver though. Any kind of long and very rigid rod would work.

author: TizianoHV
author_rank: Regular Contributor
timestamp: March 15, 2025, 03:17:04 pm
content: My lenovo laptop has some whine (not as bad as your).I tried hearing the PCB, the noise seemed coming from some inductor but it wasn't clear (no easy fix).By limiting the CPU max setting (old control panel, power) to around 70% it becomes almost silent.Obviously it won't be as fast, but good enough for normal use...

author: Sorama
author_rank: Frequent Contributor
timestamp: March 15, 2025, 04:54:51 pm
content: https://www.ti.com/document-viewer/lit/html/SSZTB09#:~:text=When%20an%20electric%20potential%20or,acoustic%20noise%2C%20or%20singing%20noise.

author: canadaboy25
author_rank: Regular Contributor
timestamp: March 15, 2025, 11:09:36 pm
content: Quote from: TizianoHV on March 15, 2025, 03:17:04 pmThis PC has the opposite issue. Under load it becomes nearly silent. At idle it screams, which is what makes it nearly unusable.Quote from: benj38 on March 15, 2025, 11:44:24 amFunny you should suggest that. I have an actual automotive stethoscope and had tried using it on the inductors with no success. However, I tried again on the caps and it seems the 3 banks of caps circled in the attached pic are all screaming. The bank next to the CPU socket has an additional 4 caps on the bottom of the board.I pulled one cap and measured it with the LCR meter and it was 10uF. So there are 2 banks of 4 caps and 1 bank of 8 caps. I measure 19V (input DC voltage) across all banks. So I should be able to replace these caps with say, two 47uF and a 100uF aluminum polymer cap? Something like this for the large bank?https://www.digikey.ca/en/products/detail/nichicon/RHS1E101MCN1GS/4991412

author: wraper
author_rank: Unknown
timestamp: March 15, 2025, 11:26:47 pm
content: Most likely you should do something only with those for Vcore.

author: TizianoHV
author_rank: Regular Contributor
timestamp: March 15, 2025, 11:30:27 pm
content: Quote from: canadaboy25 on March 15, 2025, 11:09:36 pmSame as mine. It makes noise when on idle because it periodically receives "small pulses" (background activity). This causes fast frequency jumps. If you limit the max cpu it will avoid fast changes in cpu frequency

author: canadaboy25
author_rank: Regular Contributor
timestamp: March 15, 2025, 11:36:47 pm
content: Quote from: wraper on March 15, 2025, 11:26:47 pmWhat is the reasoning behind that suggestion? They are all on the main input rail so replacing the ones near the Vcore regulator may smooth the audible frequencies enough to prevent the rest from making noise?Quote from: TizianoHV on March 15, 2025, 11:30:27 pmAh, that makes sense. Thanks for the clarification. It is definitely an option I can try. However, if possible I'd love to be able to use all of the CPU power, it doesn't have a lot to spare to begin with

author: wraper
author_rank: Unknown
timestamp: March 15, 2025, 11:43:08 pm
content: Quote from: canadaboy25 on March 15, 2025, 11:36:47 pmIt's where the vast majority of ripple current and where it fluctuates the most depending on CPU load.

author: canadaboy25
author_rank: Regular Contributor
timestamp: March 15, 2025, 11:50:29 pm
content: Quote from: wraper on March 15, 2025, 11:43:08 pmThanks, I will order some and give it a try.