[Samsung Galaxy Z Fold3] cozzi5114:
Okay, hello XDA Forums peoples! Ive been lurking here for like a decade. I feel bad for bothering you nice people, but now I'm at my wits end with this phone.

Okay, so, long story short:

Z Fold 3, let it run the One U.I. 4 update, bricked the whole phone, wouldnt come back on. This happens a week away from being out of warranty. So i get samsung to agree to let Asurion/uBreakiFix repair it (I almost always fix my own electronics, I hate Asurion, I've had problems dealing with them before, but its free so whatever). Well they get it working, i asked what they did and they were basically like 'uhhh idk'. I assume it was just an 'unplug the battery and plug it back in' kind of thing.

Anyways fast forward to a couple months ago. Im walking along the creek, i always keep my phone in my backpack for safety. Zipper on my backpack comes open some, phone falls out and directly into the water for about 3-5 seconds. Goes black within 15 minutes. Alright, so it seems like maybe the boys who worked on this didnt seal it back properly. Whatever.

I let it dry for about 4 or 5 days. Comes back on, everything works except the front screen's digitizer(which is cool for me, because the inside screen still works fine) and its reporting too cold to charge, so now once the battery runs out i have a new foldable brick! Yay! I check the battery temperature thats reported in settings and its completely fine. I hit it with a hair dryer for like 5 minutes to try and trip the thermometer, and nothing happens.

I tried some cheap shots in the dark, i replace the USB charging board, i replace the wireless charging coil, both of which have thermistors on other older samsung phones, so i figured it was a decent guess. Still too cold to charge.

So I find a schematic, or not exactly a schematic, but like a boardview, i guess. So at least i know where the thermistors are to check them. Theres about 10 thermistors on the main and sub boards. 5 of which are covered by metal shielding which i am just terrified of trying to remove, mainly because i havent done it before. So i check the other half.

The thermistors used in these phones are like inverse, so they have less resistance for higher temps and more resistance for lower temps. If one of them is dead, it will have like "maximum resistance", right? Which would report the coldest possible temperature, right? So that all makes sense, to me at least.

The 5 i can get to with my meter to check, they seem to work completely fine. From what research ive done they seem to be like 100k resistors when measured at ~70 degrees f, and i can watch the resistance go up and down when its cooled or heated past that temperature. Okay, perfect. That all checks out.

Because the other ones are under some metal shielding, i assume theyre most likely fine because any water would have a harder time getting in there. So i skip to the most expensive option so far: i buy two replacement batteries. The schematics do not include the battery, so i dont know where the thermistors are on my current batteries to check them, if that was the problem.

Well, batteries came yesterday, i pop them in, still too cold to charge. I've already ran the phone dead checking it, so i cant do any further diagnostics with the phone on. And now the most i get is a Yield sign with a thermometer in it when i plug it in.

Okay, so... Idk?? This problem is starting to get over my head. What do y'all think? It seems like my options are becoming more limited and expensive.

I can try and put a big blob of solder on the top of the shielding and pull it off to check the remaining thermistors, which seems to be how people remove those things. I also have have hot air at my disposal, which is always risky with tiny things because too high airspeed might blow components away on the board and then i'll probably cry.

It could just be a connector somewhere on some flex cable? Maybe? I mean like maybe what if one of them is for reporting temperature, and water corrosion is stopping it from sending a signal through???

Im fine with doing whatever, but i just want a charged battery first so i can recover my data before i do anything that drastic. I mean, back in the day they had 4 big pads on a removable battery. You could buy a universal samsung battery charger or rig a USB cable to charge it, but I have literally no idea what to do here. Does anyone know of some specialized battery charger that will connect to these flex cables?? That would be a gigantic help right now. Or if i knew where to get a Z Fold 3 just to pop it open and charge my battery with? Or maybe just sit there for 2 hours holding two wires to the positive and negative pins?!??!?? I dont know. Someone throw ideas at me, please!