Logicboard to LCD output problem?

MacBook Pro 15" A1286 Late 2009

Long story short:

-Initial problem: build-in LCD wasn't able to render black, instead flashing green was appearing.

-First Diagnosis: external monitor worked fine. Went to apple store / genius bar, they run their diagnosis and they only detected a battery problem (it has 400 cycles ish / nearly 4 years old) and a RAM problem (I upgraded by a non OEM apple RAM). But nothing with the logic board. Thus we concluded that it has to be the LCD.

-First attempt to solve the problem: I bought a new LCD and replaced it. But the problem still persistent.

Any idea how to solve it:

- Software problem..... ?? I don't think so.

-Logic board problem.....could be, but a new logic board is too expensive. Suggestions?

Thank you very much

Pol