It might be very rare (actually it happened to me only once, few months ago, while doing "dev work" and I had no RS232 cable, I locked myself out because of a bad rom flashing) but if your device seems dead and refuses to boot to recovery using the bottom located pinhole as trigger to enter recovery (see CWM or TWRP threads for more infos about entering recovery) don't be afraid because, unless you suffer of an hardware failure, you will be able to unbrick it using this MicroSD rescue method.

mmcinfo
fatload mmc 0 0x82000000 u-boot.bin
sf probe 2
sf erase 0 60000
sf write 0x82000000 0 60000
sf erase 0x100000 0x8000
reset

Android TV Box, something went wrong and I bricked it somehow. It dind't boot up anymore, I could enter the recovery menu from micro SD card with stock firmware on it, but it was impossible to flash the firmware, I got always the same errors, something like:

E:failed to mount /data (Invalid argument)
can't mount '/data' (Invalid argument)
E:failed to mount /data (Invalid argument)
E:Can't mount /data/log/recovery_log.txt

The easiest way to solve this, without need of short circuit of the NAND pins, is to use Amlogic BootcardMaker to make a bootable micro SD card with your device stock firmware, in my case I needed Vigica C90T 20150211 FW.

So download Amlogic BootcardMaker, download your device stock firmware, launch the application with administrator rights, select your micro SD card as removable disk to be used, tick 'To partition and Format', then Click 'Open' and choose u-boot.bin from your device stock firmware package. Now press 'Make' button and when it's done just copy all the firmware files to micro SD card (aml_autoscript, factory_update_param.aml, firmware.zip, recovery.img, u-boot.bin, unlock_autoscript).

Now insert the micro SD card in your Amlogic device and power on. You will be able to enter into recovery and the firmware will be flashed automatically. When the TV BOX reboots, remove the micro SD Card, this step is very important, wait 4-5 minutes and the update will completed. Next, follow the regular procedure and flash back to your stock firmware if this was from another Amlogic device, everything should be back to normal now.