Knob, i haven't found how to put our player into RockUSB mode (soft way).
So I used your post here :
Rockchip DEAD Player Recovery Guide
The hardware tweezers method makes sense to me.
The idea is to short some data lines together of the MLC NAND Flash so the RK270x ROM CODE will always read wrong data from the flash and will never find a valid bootloader. Then, it goes into this RockUSB mode automatically to give a chance to reprogram the whole flash.
This is very cool !!!! ( although i would prefer the soft mode haha )