from what iv'e read it is nand pins 17 + 18
found this info.
The USB port on the M8 box is a multi functional port, I found with the jumper off with my bricked box booted into TWRP on a bootable SD Card that the USB port nearest the HDMI port was detected as an ADB device without the Jumper on and when the Jumper was on it was detected as an OTG.
My situation was my box was dead red standby light and wouldn't boot into recovery, what I had to do was make a bootable SD scard using the Amlogic tools and I put TWRP with the recovery.img on an SD card.
I had to short pins 17+18 on the nand to get the device to boot from SD card, now in order to get get OTG I had the unti powered off, USB cable connected to Box and PC and the jumper next to the HDMI on, booted up tthe box with pins 17+18 shorted and the recovery button held in for 12 seconds or so, 7 seconds is to let the nand hack allow the boot from Sd card and then the 5 seconds for switching to OTG, I had a two folded issue no recovery and needing to get to OTG, normally if recovery works the box should take a few seconds to switch to OTG.....still with me on this?
Box booted with blue led but TWRP shouldn't start just a blank screen, PC detected an unknown device and I installed the USB Burn tool. It installed and loaded the world cup drivers. as part of the install.
I ran the USB Burn tool and it detected the Box on Hub1-2. I imported the Probox2 .img file and selected Force erase, below this box on the burn tool are various options for erasing the flash, what I found is in order to get my box past a 2% or 3% flash before it failed I had to deselect Erase Bootloader. The USB burn tool will fail at about 6%. This is the interesting thing once I managed to write 6% I rebooted the box left it with the red led showing but the box was detected by the PC and an OTG port, this is I think is the twist where I was going wrong.
Once you've flashed and got beyond 5% the box will be detected by the PC as an OTG port when its in standby, no need for trying to get to recovery or short the nand pins anymore. I just ran the USB Burn tool again with the unit in standby and the burn tool detected the unit as an OTG and completed a 100% flash. The trick seems to be to allow the burn tool to fail at 6% using the recovery method making sure you deselect erase bootloader in the USB burn tool or it fails at 2% which isnt enough of an erase to get u-boot sorted and repaired. Restart the box as if it's in standby run the Burn tool again and it should complete a full flash.
Crows you really need to establish whether your getting a connection, try booting to recovery, if you cant get to recovery you'll need to prepare a bootable SD card and short the nand pins 17+18 get into recovery with the USB Jumper off and see if your PC recognises the box as an ADB device, Moborobo should load drivers for a mobile ADB device. If you can establish ADB all your problem is is getting the USB port into OTG. Let me know if you can get ADB drivers installed first. No you don't need to mod the cable.
I have used Amlogic usb flashing tool before on MXQ boxes and T95Z Pro using usb A to A cable only one I could get to work was really short one 30cm long
And to get it to flash I run the burning program then connect the box. other than that i had problem like above only getting to 6%.