Ipq4018 hangs at uBoot during "sbl1_wait_for_ddr_training, Delta"

Hi,
i have a broken Device, that hangs right after power on at this stage

B -    889540 - pm_driver_init, Start
D -         2 - pm_driver_init, Delta
B -    959698 - sbl1_wait_for_ddr_training, Start
D -        27 - sbl1_wait_for_ddr_training, Delta

Normaly the next steps would be

B -    975316 - Image Load, Start
D -    152333 - QSEE Image Loaded, Delta - (297752 Bytes)
B -   1128076 - Image Load, Start
D -      1446 - SEC Image Loaded, Delta - (2048 Bytes)
B -   1138496 - Image Load, Start
D -    224138 - APPSBL Image Loaded, Delta - (458523 Bytes)
B -   1363032 - QSEE Execution, Start
D -        60 - QSEE Execution, Delta
B -   1369252 - SBL1, End
D -    677115 - SBL1, Delta
S - Flash Throughput, 2008 KB/s  (758742 Bytes,  377712 us)
S - DDR Frequency, 537 MHz

Has anyone seen such an error?
Is this a broken DDR3 Chip or some bad caps problem?

Thanks

Jürgen

Well, its failling DRAM training, so it could be anything from a voltage issue, bad DRAM to SoC-s RAM controller being damaged