For $29/mo, we provide access to advanced level technicians who will answer your questions on any Macbook board related matter to the best of their knowledge promptly & walk you through how to solve your problem so you can deliver a working board to your customer.
Do you get RAM beeps error?
Inspect RAM solders near the slot corner.
Try one module at a time, every slot separated.
Use DDR3 test card, if possible; see if all LEDs light.
Finally, put good flux and reflow MCP.
You may have luck and is only crap under it.
Heating MCP can also show an internal problem.