Yealink Forums

One of our T48G devices currently can't connect to any account and when we compared the web interface with a working phone there were different fields showing. Despite those two phones having the same firmware version it seems as there is something wrong with the upgrade procedure.
Since downgrading (flashing lower firmware version through web interface) and autoprovision doesn't work anymore - as well as countless factory resets, we figured that there was a faulty update/reset down the line.

Because of this I just tried to recover the phone as described in the yealink guide with TFTP. The connection was established, but the phone keeps reporting the the TFTP client that T48G.rom ist too large. Since it's the phone that's reporting this I can't think of any way to fix this on my side. The recovery isn't possible with Jounis TFTP client or the one from 3com. All get the same answer.

Do you have any suggestion or is this phone officially "fried"?

I'd suggest trying to load an older smaller firmware on the phone if possible.

@johnkiniston
Thank you for your replay, but I tried this too.

It happens that I could solve the issue with the help of the yealink support and wanted to share this with everyone in case you have the same problem.

It seems that the internal CA-Certificate of the T48S can cause conflicts with some SIP servers. In that case you have to access the web interface, go to "security", "trusted certificates" and set "Only accept trusted certificates to "disabled".

That's it. Now the phone works flawlessly.