Rule number 1 when you RMA - don't send anything that they don't ask for, quite often the will just take your device put it in a pile to look at later and send you a new one or one they already refurbished. They are not really interested in spending hours diagnosing - the man hours alone justifies the cost of just sending a new unit.

This is within reason of course - don't send in your unit after you drive over it with a truck and expect a new one