Accessing one control in a listboxtemplate from the events of another control in the template

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Silverlight

I have a template as defined below.

<Grid removed="#01ffffff">
                <Grid Style="{StaticResource DataItemGridStyle}">
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition
                           Width="200" />
                        <ColumnDefinition />
                    </Grid.ColumnDefinitions>
                    <Grid.RowDefinitions>
                        <RowDefinition></RowDefinition>
                        <RowDefinition></RowDefinition>
                    </Grid.RowDefinitions>
                    <TextBlock
                        Grid.Row="0"
                        Grid.Column="0"
                        Text="{Binding Facility.FacilityName}"
                        Style="{StaticResource RowDataItemValueStyle}" 
                    />
                    <TextBox
                        Grid.Row="0"
                        Grid.Column="1"
                        x:Name="tbValue"
                        Text="{Binding Value, Mode=TwoWay}" TextChanged="tbValue_TextChanged" 
                    />
                    <!-- Send Mode -->
                    <ContentControl
                        Grid.Row="1"
                        Grid.Column="0"
                        Content="Send Mode"
                        Visibility="{Binding Text, ElementName=tbValue, Converter={StaticResource myStringToVisibilityConverter}, ConverterParameter='yes'}"
                        Style="{StaticResource ReqFieldLabelStyle}" />
                    <ComboBox 
                        x:Name="cbSendModeOverride"
                        Margin="0,5,0,0" 
                        Visibility="{Binding Text, ElementName=tbValue, Converter={StaticResource myStringToVisibilityConverter}, ConverterParameter='yes'}"
                        Width="400"
                        Grid.Row="3"
                        Grid.Column="2"
                        HorizontalAlignment="Left" SelectionChanged="ComboBox_SelectionChanged"
                        Loaded="cbSendMode_Loaded"
                        DisplayMemberPath="Code"
                    >
                    </ComboBox>
                </Grid>
            </Grid>

I need to be able to set the focus to the combobox from the textbox's textchanged event. Can someone please assist me? I've been looking for a solution for most of the day.