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Motherboard issue after liquid damage.

Samsung M31S Motherboard issue

Hello.

About 4 months ago my Samsung m31s had water damage to it. At that time I dried it off and did nothing else, because it worked just fine

A few months after that, it stopped working.

I opened it and found some corrosion after cutting a heat shield , which had knocked 2 capacitor off the board(because of corrosion). I didn't solder them back but i cleaned it and the phone works.

But, the wifi, Bluetooth, SD card slot, sim, reciever, 3.5mm jack, mic all don't work.( basically the cameras and main speaker and all sensors are the only thing that work.) Is this related to one particular chip / capacitor that I should check?

I know for a fact that it is not an issue with all of things like reciever wifi etc and is related to the motherboard

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Update: 10/10/23:

after a factory reset, somehow Wifi and bluetooth work scanning the qr code from another device, but i have to literally touch the phone to the source of wifi, here another phones hotspot.

reciever speaker, etc still dont work @oldturkey03

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@windowsrage "I didn't solder them back but i cleaned it and the phone works." looks like it really doesn't. I do agree 100% with your statement that this "is related to the motherboard" and most likely all originated with the water damage.

I suggest you start from scratch and treat this the way you would treat any other water damaged device.

The very first step I would take is to disassemble your phone. Use something like this video to help you disassemble your phone. I am pretty sure you already know how to do this but like to add as much detail as possible. Take a careful and close look at all components and connectors. Truly assess the damage. Look for major corrosion, evaluate the pins in the connectors etc,. Take a look at all connectors as well as cable ends. You will have to remove all the EMI shields. If you do not remove the shields, you are not cleaning the board.

To clean any gross contamination, do not use drinking water, if you need to use water, use sterile water. Once you got any gross contamination cleaned, use 90%+ isopropyl alcohol and clean your parts some more. For a proper cleaning, use this guide. It was written for an Apple iPhone 3G but it is still pertinent to your phone as well. I can not stress the importance of a good cleaning enough, so do it over and over while replacing the alcohol after each cleaning. Do not use compressed air for the cleaning since that can drive liquid as well as corrosion particles into areas that will cause trouble later on. Also, you do not need to leave it to dry for a day. Isopropyl alcohol in the higher concentration will evaporate quickly and dissipate the water.

You know that you already have corrosion on your board so the importance for you here is the cleaning. It would of course be best to get it professionally cleaned with an ultrasonic cleaner. For as long as you have not cleaned your board , everything is just a guess.

You have already told us that your board is missing at least 2 components (" knocked 2 capacitor off the board" you are sure those are capacitors?) so we would at minimum need to see where they cam off on the board. Post some really good, focused and large pictures of your complete board (both sides) and mark the location where those component were. We can try and find the right schematics (if they are available) and see which circuit those belonged to.

If you do not have the tools, or the practice to microssolder on your board, you may need to send it to a repairer that has specialized in that. Or consider replacing the complete board. You will need to make a backup of your files/data since you will lose those.

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.

Update (09/09/23)

@windowsrage that's great! Okay, we identified the reference numbers Now let's hope we can find the right schematic. This is a place holder for the info.

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Thanks for the reply. Yes the heat shields I am talking about are actually the emi shields. My bad. I know where they came from exactly and the problem is the fact that the caps had the famous blue corrosion on them most probably due to water.

I took a clean toothbrush and ipa and cleaned all the corrosion off of the board. And yes I am sure those are caps since I have repaired a lot of phones (I font have a business but for family members) but this one in particular is having this weird issue, so I thought why not discuss it with everyone here. I will surely put some pics of the phone motherboard here in a few hours.

I have found a pdf for schematics of this phone but to be honest I don't know how to use/interpret those.

I don't wanna replace the whole board since it will atleast cost me a 100 dollars to do so. What I wanna do is use this phone as a backup since I can't rely on this phone anymore. The resale value of phone if fully working is about 100 dollars so it won't be worth it. Hence I am trying to fix it at home. I do have a oot equipment like a soldering iron flux solder wire, wick, etc but I would love go know where to start.

I will for sire make a guide for this because I totally agree that it will help others

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@windowsrage I get all of this. We are pretty understanding people on here and we all know how it goes. This is not talking down to people or belittling. We just don't know anything about the person, so we just have to all make sure we are talking about the same thing, and that we are all on the same page in the same book :-)

If you want to, and it is not a condition etc. you can attach the schematic to your QUESTION. That way we can take a look at it and hopefully help you further with this. Great techs like @tech_ni and @jayeff etc. are really good with this kind of stuff ;-)

Attach it the same way as you would picture. Use the same guide.

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Attached the schematics, I hope those are schematics because I really have no idea how they are supposed to be.

And yes I would totally agree on the fact that you don't know how the person asking the question is.

Give me a few hours, I will attach the phone motherboard pics.

Thanks

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@windowsrage no rush., we'll be here. If you add the @ and user name we'll get notified that there is someone adding information etc. Makes it easier to keep track.

It's a partial schematic for the troubleshooting sections only. Let me check if I have access to a complete schematic. The video is good for finding ways to bypass parts of the circuitry but it won't help you just yet. It's all good info but consider it incomplete for now.

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Attached the images as clear as I could.

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Hi @windowsrage

Here's the troubleshooting section of the service manual for the phone.

It has flowcharts that describes the testing procedure for all the main functions of the phone e.g. BT/WiFi flowchart is on p.25 of 38 and also board layouts showing where all the components mentioned in the flowcharts are located.

Unfortunately, it doesn't have a component parts list, so for example if a capacitor is missing or faulty its value is not shown, only its board designation.

You may be luckier if it is a faulty IC as they may have their type information printed on them.

Hopefully this is of some help.

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Hey thanks for the reply!

I have seen this and my issue is that it provides different chips for everything.

I feel like this is connected a particular chip or component because all of these chips should not fail altogether

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@windowsrage

Maybe there is more than one problem.

Water damage can cause this especially when the battery is still connected.

You can only follow each relevant flowchart in turn and check where it leads you.

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Windows Rage zal eeuwig dankbaar zijn.
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