I have slight troubles with the TL-WR740N right now. I flashed OpenWRT on it and it worked flawlessly. SSH and LUCI was working, so everything was okay.
Then, I opened the device and removed the LEDs - I am planing to use the GPIOs for some other stuff - and tried turning on the device again. But the ethernet-ports did not come up. So I checked the serial console, but also there, I did not get much output.
After a second check, I noticed that I must have removed the bootstrapping-resistors that are right next to the LED resistors. So I replaced them all with new 10k-resistors in the right places (the old ones got lost) and booted the router again. Result:
U-Boot 1.1.4 (Mar 22 2013 - 16:16:35)
AP121 (ar9330) U-boot
DRAM: 32 MB
led turning on for 1s...
id read 0x100000ff
flash size 4194304, sector count = 64
Flash: 4 MB
Using default environment
In: serial
Out: serial
Err: serial
Net: ag7240_enet_initialize...
No valid address in Flash. Using fixed address
No valid address in Flash. Using fixed address
: cfg1 0x5 cfg2 0x7114
eth0: 00:03:7f:09:0b:ad
And that's all the device does. Anybody knows how to fix it? Maybe some of the resistors should not be 10k after all?