HP 24SII - Manual (Page 127)

NOTE: Module 1 must be a serial module (i.e., Module 1 may
be occupied by any module part number other than M24SII-
V02).
3. Remove the flat aluminum plate covering the slots into which
the new module will be installed by loosening the 2 straight slot
screws and then removing the plate from the rear panel.
Save the aluminum plate in the event you have to remove the
module in the future.
4. Install the new module by sliding the horizontal card edges
along the grooves inside the module slot. Each I/O module has
a card-edge connector that fits into a receptacle inside the
Model 24SII. Apply a moderate amount of pressure to the
connector board of the I/O module until you feel the card edge
connector slip into the receptacle inside. You will not be able
to mount back plate of the I/O module to the chassis if the I/O
module is not installed all the way.
5. Mount the back plate of the I/O module to the Model 24SII's
chassis by tightening the 2 straight slot screws on the back
plate.
6. Apply power to the unit by plugging in the power cord and
depressing the power switch located on the front of the unit to
ON.