Oki C7200 Service Manual page 341

Note! The option SDRAM DIMMs must be inserted in descending order of the parenthesized type No. appeared on the label of each DIMM into the slots 1, 3, 2
and 4 (see the user documentation for details).
(3) LED Control PWB (Y71-PWB)
(4) Duplex Control PWB (V71-PWB)