Checkbox Layer On Off

[MikeJun]

What I like to do is convert layer on off dropdown box to a check box. I couldn't get it to work and wonder if someone can walk me through it.

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" xmlns:esri="http://www.esri.com/2008/ags">

<mx:Script>
<![CDATA[
  import mx.collections.ArrayCollection;
     
  [Bindable]
  public var MS:ArrayCollection = new ArrayCollection(
 
            [{label:"Census Block Points", data:0},
                  {label:"Census Block Group", data:1},
                  {label:"Counties", data:2},
                  {label:"states", data:5} ]);
                 
        private function changeH():void
            {
             //trace(msCombo.selectedItem.data);
             dyn.visibleLayers = new ArrayCollection([msCombo.selectedItem.data]);
             dyn.refresh();
            }

  private function turnLayerOn():void
  {
   //need help on this
  
  }
]]>
</mx:Script>


<mx:ComboBox id="msCombo" dataProvider="{MS}" change="changeH()" />

   
<mx:HBox>
  <mx:VBox color = '#330033'>
      <mx:CheckBox id="chk_co" label="Block Counties" change="turnLayerOn()"/>
      <mx:CheckBox id="chk_st" label="Block States" change="turnLayerOn()"/>
  </mx:VBox>
</mx:HBox>  


<esri:Map>
   <esri:extent>
      <esri:Extent xmin="-150" ymin="5" xmax="-50" ymax="68">
          <esri:SpatialReference wkid="4326"/>
            </esri:Extent>
   </esri:extent>
        <esri:ArcGISTiledMapServiceLayer
            url="http://server.arcgisonline.com/ArcGIS/rest/services/ESRI_StreetMap_World_2D/MapServer"/>
        <esri:ArcGISDynamicMapServiceLayer id="dyn"
            url="http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Demographics/ESRI_Census_USA/MapServer"/>
</esri:Map>
</mx:Application>