Have I bricked my brand new TM-AC1900?

[someperson]

I just got a brand new TM-AC1900 today. I attempted to switch the CFE in order to flash the stock RT-AC68U firmware, and I thought I followed the directions properly (enable telnet, backup the old CFE, edit the new one with the 3 MAC addresses and the WPS code, and flash back). After flashing back and rebooting, I noticed that the router still said TM-AC1900, so I reset the NVRAM by holding down the WPS button and rebooting. Now I'm stuck. The only lights that are on are the power light and the ethernet light. I can't ping or otherwise access the thing, be it in a web browser or over telnet, via either 192.168.29.1 or 192.168.1.1. I can hold down the reset light and it does flash slowly like I've read it's supposed to for recovery mode, but I still can't access anything. Is there anything I can do, or am I just an idiot who spent hours on the phone and paid $99 just to end up with a brick?

 

[someotherperson]

I was asking the same question myself couple of hours ago. Followed the steps from Engineer here and ended up in the same state as you. Only the power LED worked and no ping or web interface. The Asus "Firmware restoration" did not work either. Neither did the reset button.

Here is what worked:

1. Enable the TFTP client in Windows - Search for "features" in the Control Panel and select "Turn Windows features on or off" (I have 64-bit 8.1 pro)
   
2. Download the 1703 firmware TM-AC1900_3.0.0.4_376_1703-g0ffdbba.trx
3. Set static IP & Mask on the LAN adapter to be able to access 192.168.29.1 (e.g. 192.168.29.2/255.255.255.0)
4. Connect router port 1 and the PC
   
5. Change to the firmware folder and type this line ready in a command shell, but don't hit enter
   tftp -i 192.168.29.1 put TM-AC1900_3.0.0.4_376_1703-g0ffdbba.trx
6. Set the router in rescue mode
7. Hit enter to start the tftp upload and wait to complete with "Transfer successful ...". Wait some more for the router to reboot and get the WiFi LEDs back on.
   
8. Erase nvram again just in case
   
9. You should be able to access 192.168.29.1

Now you still cannot update to the AC68U firmware from the web interface. You would get "Firmware upgrade unsuccessfully. It may result from incorrect image ..." if you tried. But you can do the TFTP method above (5-8) with the AC68U firmware as well, e.g.
tftp -i 192.168.29.1 put FW_RT_AC68U_30043763626.trx
Note that after this update the router port will change to 192.168.1.1 so you will have to change your network settings (or use 255.255.0.0 as IP mask)

few notes:

• TM-AC1900 firmware default login is admin/password and port 192.168.29.1
  
• RT-AC68U firmware default login is admin/admin and port 192.168.1.1
• to erase nvram - turn the router off, hold the WPS button (on the side), turn power on while holding the WPS button down until the power LED starts flashing, release the WPS and give it few seconds
• to put in rescue mode - turn power off, hold the reset button down (recessed in the back), press power on, release the reset button once the power LED starts blinking
• I suspect I could have gone directly with the Asus firmware without going to the old 1703 from t-mo first
• This assumes you have already downgraded the CFE to 1.0.2.1 (US) or similar

It is probably late for SomePerson but might help someone else