Xiaomi POCO M3 shutdown suddenly, then doesn't pw on nor charging

[goriath]

Hi guys,

I have the phone in the subject, suddenly it has power off istelf and it doesn't power on no more, nor while connected to the charging adapter; it's apparently dead.

Since it's pretty easy to open, I did what suggested here:

I detached the battery, I connected the phone charger w/o battery, it turned on for a while with the battery icon, then disconnected the phone charger, reconnected the battery and it worked, the phone powered on and off regularly.
So I simply closed the phone but it turned dead again

So I reopened and did again all the procedure but while still can give signs of life while connected to charger w/o battery, when I connect the battery again and try to power on it does stay dead this time. The trick seams to work no more...

Now I checked the Li-Po with multimeter and I get 3.8V for a battery charged at 50%. Also tried continuity between the poles and it beeps (I don't know if it's normal or not)

My thought the battery is, unfortunately, good - so the problem must be something more serious

Any suggestions? There is something I can try first to try to replace battery anyway?

EDIT: forgot to say that the phone is out warranty (by 3 months...)

[goriath]

So I managed to get the phone working again

Apparently this is a common problem with this model of phone (Redmi 9T also). I followed an hint at XDA forum discussion about this issue and I removed the tiny metallic lid pictured. Under the lid there are 3 tiny caps, 2 bigger ones and the biggest one a big SMD that is an inductor (1uH), beside the latter there is an APT network IC (BGA 4*3). All I did was only remove the lid and the phone came alive and is working so far as normal.

Listen to this story - According to the user who suggest this fix there is a thermal behaviour of the bigger cap inductor which grows and hit the metal lid above causing a short. After the job done I took a caliper and I found that the gap between the cap inductor and the top inside the lid should be about 0.35mm.

The big question: is this even be possible?? Can an SMD component really grow so much under normal heating? How could it be design flaw as such?!

I made a different consideration; cap inductor can't grow as much to hit the metal lid, but could enough to get closer to it in order to start arcing

What do you think, does it actually make any sense?

P.S. BTW I still don't understand how use the inline picture attaching

EDIT: found schematics, the SMD component supposed to hit the ground it's an inductor, non a cap!

[NiHaoMike]

Any chance the can got compressed a bit from a drop?
Most likely it will work fine without the can, but you can put a layer or two of electrical tape and then a layer of aluminum or copper tape to act as a replacement shield.

[goriath]

Phone falled down several times, that's for sure () but unlikely to cause such behaviour I think; when assembled that lid is facing against the metal housing inside the phone (Al-Mg) beneath the display, so it is sandwiched in the very middle of the phone. To other side of the motherboard is mounted a plastic cover for the PCB (not pictured in the first post since already dismantled) the there is the back cover of the phone. It's well protected and very difficult that could be reached by a hit.

EDIT: I forgot to mention that the phone it's constantly used inside its own rugged cover

[goriath]

Edited the post above since it came out that the SMD component it's not a cap but an inductor instead!

[Manul]

Only a speculation, but I think desoldering the can simply thermocycled the area. It might be that it fixed a shorted ceramic cap or some solder joint.

[goriath]

Only a speculation, but I think desoldering the can simply thermocycled the area. It might be that it fixed a shorted ceramic cap or some solder joint.

That's what I thinked me also in the bunch of logic assumptions, but the user @XDA refers that heating the area w/o remove anything is a temporary fix only (that because the lid is supposed to lift due to heating, so short temporary removed), the issue disappear only when the lid is completely removed; he says repaired more than 600 units of this model of phone this way (it's a technician). There are also people who followed the same track, but not able to use proper tools, so simply teared off (yeah...) the tiny lid with a sharp cutter...and worked anyway

It seems has to do with the fact that the phone enters in a developer mode; the affected area is connected some way to test points and the shorts seems to trigger EDL state for talking directly to Qualcomm ARM CPU, this prevents the phone from normal startaup.

[Manul]

Somehow I don't believe that shorting idea. It could be loop stability issue. I assume the circuit is a switching converter. If something in layout or components selection is wrong, marginal stability is not unheard. Sometimes happens while prototyping, aka "stops working when you put you finger near". If something is very marginal, problem might be provoked by ceramic cepacitor aging, these sort of things. Hard to know for sure without in depth analysis. There are also such thing as solder dendrites (whiskers), but that is quite unlikely. I believe if higher currents are involved, they would simply vaporise and not cause a permanent short.

[goriath]

I agree and stay skeptical.
I mean CTE is a real thing but what I don't undestand, if thermal behaviour is involved, why when the circuitry cools down the phone persist into EDL and don't exit the dev mode.

What I can say the phone is still working w/o the lid, but there ia a design flaw somehow because of the amount of phones reported acting this way.

[fzabkar]

found schematics

Is there any reason why you are keeping them secret?

[goriath]

found schematics

Is there any reason why you are keeping them secret?

Sorry, here you go

[fzabkar]

There seem to be a few devices using the same IC (QET4101):

https://www.google.com/search?q=filetype:pdf+qet4101

I wonder if they have similar problems?

[pfeerick]

@goriath How did your fix go? I've also got a Poco M3, and am contemplating removing that same can, as I've pulled it down once, and had the same "temporary recovery and then refuse to power on unless the battery flattens itself" behaviour... I'm hoping now that it's been more than a few months and no comments that it worked?