Hello, I have the same problems, no chance to enter to bootloader, after connect to charging red light flashed and goes off.
Maybe there is somehow to repair bootloader via riff box ? unfortunately but there I don`t see support for this model.
Is this true that it is possible flash this unit via sd card ? I have tried prepare sd image via Ranju_sd_card but there is some errors.
I will be greatfull for any help