Agilent Technologies 8590L Service Manual page 326

Figure 7-13 A15 Motherboard with IF Section
Replacement of the A15 Motherboard
17.Position the IF extrusion assembly on the work surface with its IF
board assembly slots facing up. There is no "top" or "bottom" to the
IF extrusion; it can be installed with either finished surface mated to
the A15 motherboard.
18.Make sure that the mating surfaces of the extrusion assembly and
the motherboard are free of debris.
Chapter 7
Replacing Major Assemblies
A15 Motherboard and IF Extrusion
327