Any ideas for troubleshooting Bluetooth connection issues?

Hi @jayeff! I appreciate you took your time to write such a detailed answer. I could have provided more information in the initial question, but I didn’t want to make it too long and boring (couldn’t avoid that this time!).

> Has the phone been dropped or gotten wet at all?

Yes. The connection issues happened some time after a hard drop on the floor. Despite having no external damage (thanks to its case and glass film), I guess it’s possible the phone suffered some hardware damage. I disassembled the phone yesterday hoping to check for any visible damage.

Apart from the Bluetooth connection issues, the are some rare (twice every month or so) issues with cell radio connection. In those cases, the OS shows there is no signal or no SIM connected. That hasn’t been too bothersome, since it usually fixes itself within a few minutes or after a reboot.

> When you say “….a full software reset”, do you mean that you restored the phone with a factory reset, back to its default factory condition and tried it without any user downloaded apps installed on it?

I tried a factory reset. However, I restored the dozens of app in the installation process. Thus, I did not try without all those downloaded apps. A few minutes ago, I tried using a Bluetooth speaker with the phone on Safe Mode. It did manage to connect to the speaker, but the connection was stable only for a few minutes. After that, audio started getting choppy and eventually the connection was broken. I couldn’t try connection to my watch, since Safe Mode blocks the Zepp app from opening.

> What is the WiFi connection like, is it a stable connection or does it suffer from drop outs? (...)

WiFi connection is stable. I rarely (once per month or so) have WiFi connection issues, and when they do happen, I think its more likely they are caused by the router.

> If the WiFi also has problems, maybe check the antenna connections in the phone. (...)

Thanks! I guess the black antenna is for cell radio and the white antenna is for WiFi. Is that right? Yesterday I did manage to disconnect and then reconnect the terminal for the black antenna shown in that image you shared. I tried doing the same with both ends of the white antenna, but they were so firmly connected that I gave up in order to avoid breaking things. Despite no clear issues with WiFi, I could give it another try next time I disassemble the phone. From what you explained, it doesn’t seem to make sense disassembling the phone again just for that.

Hi @jgsiqueira

If there are no problems with the WiFi then most likely it isn't an antenna problem.

GSM uses different antennas to BT and WiFi which use the same one as they both operate on the 2.4GHz band.

Here's what the GSM antenna looks like in your phone. It's part of the buzzer module.

it's a pity that you didn't try it in factory default mode only i.e. no downloaded apps, only pre-loaded default apps, just to isolate whether it is a hardware or software problem. If it also failed in factory default mode only it would most likely be hardware,. if not then it is software.

Try wiping the cache partition (scroll down and use method 3 in the link) and then check if the BT connects and is holding.

All the apps that you downloaded and installed leave temporary data in the partition and sometimes this can interfere with the operation of the phone if the data is corrupted somehow or even buggy.

If still no good you may have to factory reset it again and try it then. Backup the phone to the cloud or a PC first so that you can restore to what is was before you factory reset it.

If it is hardware then you will need the schematics/service manual to hopefully find out what's wrong.

i didn't download it look so hopefully it is OK

Hi @jayeff. Thanks again!

I tried wiping the cache partition but it seems that this option in not available with MIUI 11, neither in recovery mode nor within the settings.

I'll try a new factory reset as soon as I have some spare time and patience. I'll share the results here as well.

Thanks for the schematics you shared.

Wish you the best!