Use the DropUp method to hide the drop down portion of the control. Use the DropDown method to show the drop down portion of the control.

The following sample shows the drop down portion of the control:

Private Sub CalcCombo1_KeyDown(KeyCode As Integer, Shift As Integer)
    If (KeyCode = vbKeyF2) Then
        With CalcCombo1
            .DropUp
        End With
    End If
End Sub