Thank you for the replies.
The device provides output log like this
BCM74130011
012
K1
K2
K3
K4
K5
Shmoo Version=3.8
DDR Freq=0x0000018C
%00000001%
G=00000000 R=00000000 W=00000000 00000020
K6
F
As you can see it starts with CPU identification( Broadcom 7413). Then it continues with some checks( K1, K2, K3,K4,K5) and then it seems to start checking DDR. K6 seems to be the last check and then F( probably means Failure)
Some googling helped me find out that it should mean DDR problem or a part linked with DDR(e.g.DDR termination regulator)
Problem is that the CPU ( BCM 7413) is made by Broadcom which does not provide datasheets.
Replacing DDR without the real reason( that the DDR is faulty) does not seem to me the best idea. Yes, I already reflowed BGA DDR but no success.
Once again for your suggestions and feedbacks