Hi,
I have a GL-AR300M-ext which is refusing to boot. I opened it (btw these routers are really nicely accessible, kudos, Gl-inet) and hooked up the serial. In console I only get this:
U-Boot 1.1.4-g36de7573-dirty (Jun 1 2017 - 09:14:12)
DRAM: ath_ddr_initial_config(219): (16bit) ddr1 init
4 MB
Any tips where to look? Is it really fried?
Few more details:
It was running OpenWrt 17.04 from NOR at that moment and I had two 20dBi omni antennas on it. At some point the wifi just disappeared and based on the LEDs and the suspiciously low power consumption the router appeared to be not booting at all. Which lead me to hooking it up on serial as described above.
Any troubleshooting ideas are welcome, not afraid to measure/solder on the board 
The router should have 128MB ram. Now for some reason it only shows 4 so it should be a problem.
When you use high gain external antenna, don’t detatch or attach the antenna when the router is powered on. This will damage the router.
The router is damaged I think. Generally no way to save it.