How easy is it to replace a motherboard in a notebook?

[MowrMowr]

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I asked them if there was a possibility that there was some problem causing the motherboard to go bad, as I had just had it replaced. They said the most likely scenario was that when I sent it in for warranty service, the motherboard was replaced with a used board that was on its way out.

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96% chance there's something causing the mobo to die
4% chance that scenario took place

Expensive lesson forthcoming