Coil whine

[khumarahn]

What is the right way to fix the step-up inductor whine, as here: https://olimex.wordpress.com/2017/11/03/teres-i-update-first-feedback-from-our-customers ?

I have two screens now (thanks Tsvetan!). The noise only appears with one of them, and only on medium brightness.

This is not so much annoying, but an interesting problem to solve. (I would not want somebody else to do this for me, it has to be DIY.) The blog mentions that one could add a 100uF capacitor. I do not understand the main board schematics, but I have soldering equipment and I am willing to take a risk.

Would it help to replace/add a capacitor or the coil, and if yes, then what exactly needs to be done?

[khumarahn]

The hardware schematics on github seem a bit outdated. The mainboard revision there is B, and there are visible differences with rev C.

I tried to understand what I can do with the capacitors, and it seems there aren't many options. Take the capacitor right before the step-up inductor (C205, 22uF). It is very small, 1.6mm, and there aren't many replacements of this size. I can find only one of higher capacity (47uF):
https://uk.rs-online.com/web/p/ceramic-multilayer-capacitors/9015332/

I can stack two of these on top of each other, this will give me 94uF. I wonder if this makes any sense.

[Brian]

Seems to are C204, C206. You may try to solder two more capacitors 47uF/25V in paralel on them

[khumarahn]

I took a photo of my board, slightly better quality than those one can find on the internet:


They changed C204 and C206 compared to Rev B. They are not 0805 any more but 1206 (i.e. 2mm vs 3.2mm long), and I do not know how to check the capacity (other than ask here).

Is 25V enough? There is a mention of some 36V in the schematics for rev B, in the list these caps have 50V spec.

[Brian]

I have measured 22uF each and 12V on DCDC output. Refering to display electric absolute ratings: Converter input voltage = 26V, Recomended - min = 5V, Typ: 12V, Max: 21V, so 25V spec. seems to be ok.

[khumarahn]

Thanks! :-)

I can by these 47uF capacitors:
https://uk.rs-online.com/web/p/ceramic-multilayer-capacitors/7883060/
and replace.

[grmpf]

Hi,

I want to bump this topic up as a main question is still not answered completely from Olimex side. I'd like to stop the coil whine by replacing/adding a capacitor on my Teres. In this blog entry: https://olimex.wordpress.com/2018/01/19/teres-i-diy-open-source-hardware-modular-hackers-laptop-update/ Olimex told

adding bigger capacitor 100 uF in parallel to C204 was solving completely the issue

@Olimex: Could you please elaborate on that capacitor replacement: what is the capacitor voltage and where could we get such capacitors?

Thanks!
Jörg

[LubOlimex]

Just change C206 with 100uF or bigger - this is shown in the picture at the blog post (before the change C204 and C206 were the same).

So search for capacitor 100uF for 16V in 1210 package. The rest of the parameters are irrelevant and personal preference. Of course, you can also use bigger capacitor in slightly bigger package if you have such available.

[grmpf]

Thanks!

[tedp]

I received a Teres yesterday and it has significant coil whine - when the brightness is anywhere except minimum or maximum (or off). It looks like C204 & C206 are different sizes so it should be the bigger capacitor and shouldn't have this problem? I'll pop the bottom cover off - hope I don't break any snaps - and see if putting some glue on L11 helps. It should be OK to use hot glue right? I don't have any adhesive pads or super glue, although maybe it's better to try them first. The sound is quite loud so I doubt that an adhesive pad alone would absorb all the vibration anyway.

(referring to: https://olimex.wordpress.com/2018/01/19/teres-i-diy-open-source-hardware-modular-hackers-laptop-update/ )

Update: I checked the board & schematic, I think there's a problem with the solder on C204 & C206 where the two close ends have been bridged with solder and are therefore connected in series and having 18 µF combined capacitance, rather than 122 µF as intended. I have contacted support.

[LubOlimex]

Hey,

I received your e-mail and pictures.

The problem is that you still have coil sound... The soldering is fine.

Do not separate the capacitors. It is not a problem that they are connected, this side is common. I attach an excerpt from the board layout – I've outlined the two capacitors and you can see the wire that connects together their VDC side (fat red wire between "1" side).



Best regards,
Lub/OLIMEX

[khumarahn]

In an attempt to get rid of the noise, I have replaced both C204 and C206 capacitors. The replacement is TDK 47uf https://uk.rs-online.com/web/p/ceramic-multilayer-capacitors/7883060/

This had almost no effect on the noise. Maybe it got a little less loud, but I am not sure. Then I added two more 47uf capacitors, one on top of each. The sound got a bit quieter, but again not significantly.

The whine does not appear with my previous screen, but I have broken it recently.

[khumarahn]

A picture:

[khumarahn]

I fixed the coil with the superglue, and the noise got much quieter, but it is still audible. I am looking for a solution.

Maybe I could replace the coil with another one (if I manage to un-glue it from the board)?

upd: despite the superglue, the whine is back. It has to be fixed before I can use the laptop comfortably.

[khumarahn]

I tried to find a replacement coil and could not. Where do you source them from? Do you know of anything suitable that would fit the pcb?

Why is there still noise despite the four 47uf capacitors?

I got used to a light laptop with good battery life, which is supposedly repair friendly. It would suck if this problem is not fixable.