Dear @LSL,

LSL wrote

after updating the firmware the device appears as offline, 

Any screenshots? Do you mean the ER7206 router is shown as "Disconnected" state on the controller?

Or the Controller itself is shown as "Offline" from Omada Cloud site (https://omada.tplinkcloud.com/)?

The router will reboot after the firmware update, it may take a few minutes to get restarted.

Perhaps you need to wait a couple of minutes and check again.

Dear @LSL,

LSL wrote

the pwr light is on but SYS OR WAN/LAN PORTS DOES NOT TURN ON THE LIGHTS.. THE ONLY THING I DID WAS UPDATE THE FIRWARE FROM OMADA CONTROLLER..

Which controller version are you using, and are you still able to access your Omada Controller?

Can you recall the previous firmware version of your ER7206, and which firmware version you are trying to upgrade to?

If you can access your controller, please go to Devices page, click the router name and check the current Firmware Version under Details.

Dear @LSL,

LSL wrote

Model:

TL-ER7206 v1.0

Firmware Version:

1.0.0 Build 20201105 Rel.77675

 

Today I tried to use the emergency mode but no luck, I followed the steps to the letter, I only got lights for two seconds and the device has no response.

The emergency mode is added since the firmware update of 1.1.1 Build 20210723 Rel.64359, check this post for details.

For your case, it seems that the router is bricked, you may contact the reseller for a replacement.

Dear @LSL,

LSL wrote

I had saved a TL ER6120, I have installed it and I was able to achieve load balancing, but now omada controller appears disconnected from omada.tplinkcloud.com.
I try to enter from a computer connected to the sg3428mp switch but I cannot enter, is this because I have the tl-er6120 router at 192.168.0.1?

Both the TL-ER6120 and the SG3428MP switch use 192.168.0.1 as the default LAN IP address, if they are connected in the same network, it's suggested to change the IP address of the SG3428MP switch (for example, use 192.168.0.2) to avoid IP conflict.