820-3115 No RAM, 3 Beeps

Hi, need help with a Macbook Pro 13", 2012, motherboard 820-3115.

Board boots and don't detect RAM, have try different known good RAM and nothing.
Board don't have liquid damage, the problem just appears one day, not gradually, no freeze screen or ramdom rebooting before.
PP1V5_S3_DDR is 1.5 volt
PP075_S3_Mem also normal
PP0V75_S0_DDRVTT also normal

Anything I need to test before thinking is a CPU problem?
 
Yes, I tested one RAM slot at a time, the original RAM of the Macbbok is good, tested in another board and works fine.
And yes, my known good memory I use to test is SK Hynix 2GB PC3L-12800S-11-13-C3 and I also tried Samsung 2GB PC3-10600S-09-11-B2, also good, that memory is from other Macbook A1278 with the same board.
 
2Informaticos, thank you for your reply, I start touching the pins with my tweezers and pins 2 and 6 were loose. So lots of flux and hot air, I saw the solder melt, I ultrasonic the board and now Mem slot B is working, but Mem slot A, don't work, if I put a memory in slot A I get 3 beeps.

Mem Slot A pins go trought the board, so I think I?m having another issue now. Or still same problem and I have to solder again?
 
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