Hello I finally found uart pins and could reset root passwd...
But the pb is now that the rootfs supposed to be mounted mtd2 in yaffs2 seems to be destroyed - so kernel panic etc...
I had access to another one (same) but, too much newbie on this art, I don't even know how to create/extract and restore cleanly a yaffs2 image through u-boot.
The model is in fact a DM-SCB405IDP-V10-E.
Prog Version : V1.0.8 Build 201805142139-r3091D
Ctrl Version : MiniPtz_V2.1.1_Build201701092117
Web Page Version : 1.1.1 Build 20180514P
Could someone show me the best way to recover it?