Oki 2426 Series User Manual page 557

To insert the memory modules into the slots:
If you are installing three 256 MB modules (the maximum
amount of memory), the memory modules that were
originally installed must be removed.
The printer may not operate correctly if the modules are not
firmly seated.
4. Push out the white tabs at either end of the socket.
5. Lift out the board.
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CAUTION!
Executive Series 2426 Printer Family User's Guide
Accessories • 557