Sony Vaio Keyboard problems

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I have a sony Vaio PCG FR415B laptop and 2 of the keys have stopped working (the a and s ) can some kind person let me know what other models of sony laptop models would fit mine........ I have seen several keyboards on Ebay with the same PCG but the second half is different........ i would also like to know how best to fit a new keyboard if I am lucky enough to find one. I would be so grateful, as I cannot afford to pay a lot of money. Thank you dustyshaw5@hotmail.com