T-Mobile branded TM-AC1900 wireless router is a rebranded asus AC-68U.
There was a very good deal in around 2016. And it can be flashed into Asuswrt Merlin firmware, one of best mod firmwares for Asus routers.
But Asus added a check to its latest 3.0.0384 series firmware to block a modded TM-AC1900 from upgrade/download to other build version, and to use its AiMesh feature, which is now supported by the latest firmware builds (384+). Asus have recently changed their code to prevent this, and this change has been carried over into the Merlin builds.
The consequence is, once you flashed the firmware to Asuswrt merlin firmware 384.x, you cannot upgrade/downgrade firmware any more, it will stays at the version of 384.x for ever.
Fortunately, I have found a solution as following. The T-Mobile certificates have to be wiped from the mtd5 partition. This must be done before any newer version of ASUS firmware is flashed. As of this writing, the firmware included in the bayareatechpros guide is 18.104.22.168.376.3626, so the steps below should be performed when this version is running on your router.
From a wired connection only. AT YOUR OWN RISK
Download 384.x Newest from here: https://sourceforge.net/projects/asuswrt-merlin/files/RT-AC68U/
Extract download for: .trx file
Download Asus utility: ASUS Device Discovery version 22.214.171.124:https://www.asus.com/us/Networking/RT-AC1900/HelpDesk_Download/
EDIT: Do a factory reset through the GUI before proceeding. (you can enter SSID and Password for minimal setup)
You need to enable SSH under the Administration tab / SystemEnable SSH LAN + WAN LAN onlyAllow SSH Port Forwarding YesSSH Port Allow Password Login YesEnable SSH Brute Force Protection No
Set computer IPV4 to static IP: pick number greater than router?s IP: (Example, 192.168.1.70)
From Putty run these commands, one at a time, (so ?enter? after each line of code.)( you need your current router login ID and password ID and router IP address)
# Backup MTD5 (dd produces identical bin)cat /dev/mtd5 > /jffs/mtd5_backup.bin# Copy and backup mtd5_backup.bin from router using scp# From host: scp firstname.lastname@example.org:/jffs/mtd5_backup.bin ./# Mount MTD5mkdir /tmp/asus_jffsmount -t jffs2 /dev/mtdblock5 /tmp/asus_jffs# Wipe mtd5 files and rebootrm -rf /tmp/asus_jffs/*sync && umount /tmp/asus_jffsrm -rf /jffs/.sys/RT-AC68Unvram unset fw_check && nvram commit && reboot
After router rebootsUsing Device Discovery log into router and flash new .trx from within the router?s built in GUI utility.
If you were on 192.168.29.1 to access control page the above will now revert to stock 192.168.1.1