Last week my Fairphone 3 stopped charging in the evening (battery 65%) and next morning it was completely empty and hot. The phone looked like dead. I opened it and saw that all the (ground?) pads on the Display module looked corroded and the small (ground?) contact on the bottom module itself looked corroded too. I cleaned everything, assembled it all again but phone remained dead, whatever cable/charger I tried.
Then I ordered new bottom module and battery. But when I put in the battery, it started to get very hot again, in fact, it started to melt. When looking at the old battery, I also saw some melting happened. See attached picture.
Any suggestions?
Ouch, that sounds very bad.
So even after cleaning it’s still ocurring?
Do a backup ASAP if you still can.
Look on the side of the motherboard. Can you photograph this?
Hi, phone is dead, no backup possible :(. I will try to make a picture of the side of the motherboard. Can you indicate where exactly to look at?
I was interested in the contacts on the motherboard facing the battery, and their state. You mentioned corrosion.
And how do you mean by dead?
With dead I mean it does not boot. If I leave the battery in, it will completely drain and melt. Connecting to a charger does not trigger any action (LED whatsoever). Should it be able to boot w/o battery in when connected to a charger?
On the attached picture, I indicated with red circles those pads that were corroded. Specifically the one connected to the bottom module looked bad, as does the contact on the bottom module itself that connects to this pad (I can only upload 1 picture at the time)
this picture shows the contact of the bottom module that was corroded. I cleaned it in the mean time, but I also replaced the full module. And the contacts to the battery are all clean (forgot to mention that)
If it is dead, then how does the battery get hot? I’m not sure I get the full present state of the phone.
Can you get a nearby angel to have a look at it?
Let us try something: open the phone, remove camera, top module, speaker module.
What is left is the following: motherboard, bottom module, and add the battery. That’s it, nothing else. Try to plug that in.
Thanks, as long as I know there is not an angel nearby. But I went 1 step further: I removed the motherboard from the phone and did some more inspection. With bare eyes I can see some stuff which looks doubtful. I will take it to work tomorrow (we have some nice microscopes there 
and then I will try your suggestion.
By the way, you are right: if the battery is melting it is indeed doing anything. There is really a hole in it now! With dead I mean no LED no vibration, nothing on the display, no response to any button.
To be continued tomorrow.
a hole? in the battery? My feeling is some electrical short is happening. If you changed batteries and bottom module, it must be the contact with the battery, on the side of the motherboard. this is not good. I’ve never seen that before. Please document it with photos !
Don’t use it, source a replacement. Battery’s protection circuit might have failed.
Battery is brand new. And fairphone did not allow me to use the gift card that I received when buying the phone. And on my question why? They are allready taking two weeks to answer.
Pretty bad service.
The still indicates around 4V between + and -. So I believe it must be in the motherboard. I will check that in detail tomorrow.
I opened and inspected the motherboard. I found some heavy corrosion near the Qorvo TX-RX module. I cleaned it, but I could see some of the SMD components did not have metallization anymore on one end. I put back the bottom module only, motherboard and battery. Unfortunately, the battery still gets hot, and no repsonse from the phone. So I am afraid it is end of life.
Some update: when connecting the battery to the motherboard only I could see with my IR camera that one SMD component went very hot. I removed the component (it looks burnt), connected the motherboard, bottom module, battery and display and guess what? It boots again. Will save my data and see how the removal of SMD has damaged the functionality
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Good catch! It’s a short or, from the looks of it, a capacitor that blew.
It looks like to be around the RF transceiver, so the chip that processes the 4G signals. Maybe you don’t have mobile data anymore?
Tonight I saved all data. Tomorrow I will fully assemble and test all functions
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lucky. I do a backup every week. I am a strong believer in Murphy’s law.