Download latest Android 4.2.2 Jelly Bean stock firmware for Onda V812 tablet from here or here. Download another Onda firmware from here.
Archive name: V812 Core4_v3.3.1_v1
Archive file size: 367 MB
Support: Allwinner A31
Model: Onda V812 tablet
FW version: V3.3
Pixels: 1024 x 768
Build number: fiber_onda809q9-eng 4.2.2 JDQ39 20131119 test-keys