TM-AC1900 modded asus AC-68U cannot upgrade under Asuswrt Merlin 384.x

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 3.0.0.4.376.3626, 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 1.4.8.2:
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 / System
Enable SSH LAN + WAN LAN only
Allow SSH Port Forwarding Yes
SSH Port Allow Password Login Yes
Enable 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)

https://www.putty.org/

# 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 admin@192.168.1.1:/jffs/mtd5_backup.bin ./

# Mount MTD5
mkdir /tmp/asus_jffs
mount -t jffs2 /dev/mtdblock5 /tmp/asus_jffs

# Wipe mtd5 files and reboot
rm -rf /tmp/asus_jffs/*
sync && umount /tmp/asus_jffs
rm -rf /jffs/.sys/RT-AC68U
nvram unset fw_check && nvram commit && reboot

After router reboots
Using 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

Reference:

1. https://slickdeals.net/f/9330575-asus-tm-ac1900-wireless-ac1900-dual-band-gigabit-router-59-free-shipping
2. http://koolshare.cn/forum.php?mod=viewthread&tid=59540&highlight=%E7%BE%8E%E7%89%88
3. https://www.snbforums.com/threads/asuswrt-merlin-384-8-is-now-available.50189/page-22
4. https://www.snbforums.com/threads/the-tm-ac1900-is-not-supported.48056/
5. https://www.techpowerup.com/forums/threads/asuswrt-merlin-on-converted-tm-ac1900-problems-upgrade-path-to-384-6.246293/
6. http://www.bayareatechpros.com/ac1900-to-ac68u/