4G not working on phone

[starLED]

I have two exactly the same phones NOA Vivo 4G.

Phone has an option to turn on/off 4G internet.
On one phone 4G is working, but on the second one when I turn on 4G internet stops working.
It shows H+ signal (on other shows 4G) and upload is working (up arrow is blinking) but download doesn't.

I have disassembled the phone to check if antenna is bad, but I don't see any issues.
Is this a hardware or software issue?
Maybe I can replace antenna.

 

[rjenkinsgb]

The RF modem settings are controlled by data sent from the service provider.

Are they using the same service provider? You can ask them to send updated settings to the phone.

If you are moving the SIM between phones, is the working phone the one the SIM was originally activated in, by chance?

 

[starLED]

The RF modem settings are controlled by data sent from the service provider.

I have moved two SIM cards from the working phone to non-working.

Are they using the same service provider? You can ask them to send updated settings to the phone.

Yes, it's the same provider.

If you are moving the SIM between phones, is the working phone the one the SIM was originally activated in, by chance?

Yes.

 

[alec_t]

Have you tried a factory reset of the non-working phone?

 

[starLED]

No. I am reluctant to do that.

 

[rjenkinsgb]

I'd definitely ask your provider to send a configuration update to the non-working phone, whilst that has the SIM in it.

 

[starLED]

I did reconfigure APN, no change.

Funny thing is, I moved back SIM cards to non-working phone and also there is no 4G.
I also tried brand new SIM card in working phone, and no 4G also.

Maybe it's a provider issue, or some problem with signal coverage.

 

[starLED]

Today I noticed that I don't get calls even though the signal is full on both SIM cards.
I tried to make a call, and it doesn't ring, just silence.
That happened couple of times. 4G was turned on.

I turned on/off Airplane mode, and it worked again.

If I turn off 4G, then phone works better and internet is good most of the time, though is just H+.

 

[ahsrabrifat]

Swap SIM cards between the two phones. If the problem follows the SIM, Maybe there is an issue with your carrier or SIM card. If the faulty phone still has an issue with the working SIM, then it's not a SIM or network issue.