1- Built a custom image using image builder " make image PROFILE=TLWR740 "
RESULTS: Flashed = OK. After reboot = OK.

2- Built a custom image using image builder with command "make image PROFILE=TLWR740" but this time I added FILES="/Files to the command" (/etc files in it)

RESULTS: Flashed = OK. After reboot = Sys LED blinking endlessly.

Symptoms:
-  Sys LED blinking speed 4-5 times / sec
-  Tried fail-safe but it doesn't respond to the reset button.
-  Switch is working but the led of that port doesn't turn on (connected to pc with lan cable)
-  Ping to 192.168.1.1 = no response

Unlike usual brick cases with this particular router,  The switch is not completely dead so it seems it does boot into OpenWRT a bit and then panics.

I noticed there was an error in build log: ./etc/rc.common permission denied. Yet the build was successful.

I have USB-TTL which helped to unbrick it few months ago but I don'twant to go through that process again. Is there anyway I can fix it without opening the case? But the most important thing is to identify the reason behind all this.

(Last edited by farrukh on 3 Jul 2014, 13:12)

Well, due to no answer from community. I had to fix it with conventional USB-TTL method.

did you save some kind of serial bootlog or logread? that could help understanding what went wrong..

No serial log. Did it blindly with just 2 pins (tx+gnd). I figured out what went wrong. The files I included during the make image command were the culprit.

Since you posted this in "Hardware Hacking" you must use your rs232-TTL cable