Board not booting

i have a rockpi s without on-board storage. after an upgrade the board stopped working. using the UART i can see just:

DDR Version V1.26
REGFB: 0x00000032, 0x00000032
In
589MHz
DDR3
Col=10 Bank=8 Row=15 Size=512MB
msch:1
I tried a different uSD card with all available OS images with no result.
Can anybody give me some debug tips or hints as to how the board can be repaired? It does not seem “dead” - more or less just bricked?!?!