Galaxy S8 - No cellular signal

Perhaps you may have forgotten to plug the antenna cables back in from the charging port to the logic board?

Also if some antenna contacts are broken on the logic board that connect to the plastic antennas that go over the logic board and are usually held down by screws that can be your issue too.

Refer to step 21 of this guide:

Sostituzione scheda figlia I/O Samsung Galaxy S8

defective charge port if the cables are fully connection try a new charge port also reconnect the antenna connections just in case

I have tried all the solutions did not work for me

Then I took the phone apart and looked In side

on further investigation I found a loose flex cable on the mother board where the main antenna connects by the charging port on the left

This Straight away fixed my gps location problem.

I think the obvious thing is to disassemble the device and put back together methodically ensuring that all connectors and antennas are replaced properly and that the antennas are connect to the correct points on the board and not swapped over.

Factory reset the device, update the software and test again.

If none of that works I would assume that there is some damage to the bottom board and would swap that out. Once swapped out I would software the device again and then test.

If all of that fails it really needs to go to a professional who may diagnose a PCB fault.

I got a similar problem I swapped everything including the connection cable, speaker and the USB c port and I still can only get edge connection after a screen swap

There's one solution that worked for me. I just changed the Sub PBA (charge port) and it worked.

Make sure you connected the antennas in their according places. There could be the possibility of a damaged charge port. Make sure you replace it with the correct version that corresponds to your device as there are a couple different variants. Look up the model number either on the back or in the settings and find the charge port that is compatible with that model. Good luck!

The problem is the charging port. First go in settings and check if imei number is showing. If it dosen’t then reconnect the charging port then the signal and imei would return

Perhaps these two cents may help you all. I too had this issue with my Samsung Note 8. I made sure my connections were solid and it still didn’t work. Gratefully, my old charging port worked outside of the actual usb port itself. I compared the new one versus the old one and my old one would connect to the network and the new one wouldn’t. That’s when I checked the model numbers. My device is the N950U model (for the US) and the new charging port I was trying to put in was the N950F model (for Europe and Australia). Oops! Verify that first and see if that may be the conflict. Hope this helps!

UPDATE: Received the replacement N950U charging port and the data reception is flawless.

Signal problem

Repairing

It appears my cheap, replacement, S8 plus screen/frame is missing the gold underside, aerial contact pads (6 of them) plus a silver contact pad . I'm sure this is why very poor signal. Don't know how to remove from old frame. Compare your original frame with replacement frame.

Guys, lemme tell u a bit my case, I bought a used G950F (Global single SIM version) here in Colombia, noticed it hardly grabbed any network, almost never showed 4G and even if it did show on top, or H or 3G, data was miserable, pretty much didn’t work, would BARELY send a message, like 5 mins after you “sent” it, ofc wouldn’t load a full website/video/etc. I disassembled and noticed that, you know this phone has two boards, the main and the bottom/charging board (also controls speaker, lower mic and I guess something related to signal) anyway, in the flex cable I noticed it said G950U (USA Unlocked version), so in short, I guess probably the charging port died or smth and they put a 950U charging board with a 950F mainboard, seems they’re not compatible. Found a 950F charging board, my signal is KINDA back, like, it WORKS at least, sometimes, like ofc in open street 4G is fine, youtube etc, but it still drops from 4G to H or 3G all the time, altough it WORKS in those networks now (before it showed the icon but no real service), I’m digging why it’s now MUCH BETTER but far from my last S7 which was pretty much permanent 4G full signal full speed anywhere. Will post updates

If you are connected to a wifi network, you are using the wifi. Are you stating that your cellular data only works when it's enabled but not connected to a wifi network? Do you see the 4GLTE icon at the top of your screen? Check Settings>Wirleless&networks and ensure the state of the cellular network is enabled. If it is and the cellular data is not working you can try to reset the network information by opening up your dialer and entering ##72786# and tapping yes. This will take you thru the activation steps once more and you should have your cellular data working once more.

I also had the same issue with my phone, i tried so many ways but in vain, suprisingly this method worked out for me.

Go to Settings>>Apps>>Sim Toolkit>>Storage.

and then clear data and restart phone.

Hope it helps

Hey @Gary Dale, any luck?

My Galaxy S8 (950U) was peacefully sitting on the table when it suddenly decided to give me a “no network connection” sign and disconnected itself from WiFi. I managed to reconnect to WiFi but the no connection problem (crossed circle icon on the top right) still remains. Otherwise, the phone looks and functions like new.

As i now opened the phone (for the first time in 4 years), i see that some labels have turned pink which might indicate a water damage. Due to Corona, i regularly washed my phone with a soap under the running water (NOT submerging). As the phone has a IP68 rating, it is strange that the water got in. Anyhow, the water damage is only a hypothesis and it might not be related to the issue.

QUESTOIN: What swappable parts could be culprit and in what order?

First, i will try to by a replacement daughter board (with chagrin port and two antenna cables). If it doesn’t work, I’ll try to replace the loudspeaker plastic with the baked-in antenna lines. Lastly, if all this fails, I will need to replace the motherboard. Does this sound rational?

1 000 thanks!

I bought a used S8 and noticed signal was extremely $@$*!&, no 4g most of time, I opened and realized the mainboard and charging board didn't match, main was 950U and the charging board was 950F. I guess the guy broke the screen at some point and swapped his old board U but to an F screen/frame/charging board.

I replaced the charging board for a 950F so it matched main board and the problem is fixed. Btw je really careful with the broad connector between mainboard and charging board. The first replacement charging board F I screwed up bc i was trying to connect them kinda “blindly" and ended breaking connector, whereas the speaker would only work when I pushed the connection manually, had to buy a second charging board F and this time carefully connecting with mainboard gently and before puting the whole thing inside phone, so I could seeand handle the connectors correctly and not blinded

Try replacing white flex cable that connects main motherboard to the charging board, it helped me.