T28P and multiple EXT39 modules crash/lag the phone

[Yealink Support]

Hi Marcello,

Please try below steps:
1. upgrade the firmware to 2.72.0.30 version fisrtly.
2. If you phone use POE supply power, it only can support two EXP39 module. So please plug standard power supply which is DC 5V/1.2A in the EXP39.
3. If it still fail, please set the SIP Session Timer T1 (0.5~10s) to 2s, click confirm to accept the change.
4. set your pbx server T1 timer to defualt. if it fails, raise the time.
5. please try set BLF to 80 extensions, don't more than 100 extensions.
6. register your account use UDP transmission mode and try again.

BTW, may i know why do you need set 120 BLF key?
And if you set the other type of the DSS Key,like speed dial, call park and so on. Can EXP39 work well?

thanks