check checkbox on populated dropdown value selection via javascript

i got for the 6 Scenario what i want to do 6 checkboxes:

    <tr style="height: 21px;">
<td style="width: 25%; height: 21px;">COB</td>
<td style="width: 25%; height: 21px;"><input name="COB" type="checkbox" id="COB" value="1" <?php if($_GET['COB'] == '1'){  echo 'checked="checked"';}?>/>           </td>
<td style="width: 25%; height: 21px;">SMT</td>
<td style="width: 25%; height: 21px;">  <input name="SMT" id="SMT" type="checkbox" value="1" <?php if($_GET['SMT'] == '1'){  echo 'checked="checked"';}?>/> </td>
</tr>
<tr style="height: 21px;">
<td style="width: 25%; height: 21px;"></td>
<td style="width: 25%; height: 21px;"></td>
<td style="width: 25%; height: 21px;">BGA</td>
<td style="width: 25%; height: 21px;">  <input name="BGA" id="BGA" type="checkbox" value="1" <?php if($_GET['BGA'] == '1'){  echo 'checked="checked"';}?>/> </td>
</tr>
<tr style="height: 21px;">
<td style="width: 25%; height: 21px;"></td>
<td style="width: 25%; height: 21px;"></td>
<td style="width: 25%; height: 21px;">  TSOP Typ 1 </td>
<td style="width: 25%; height: 21px;"><input name="TSOP" id="TSOP" type="checkbox" value="1"<?php if($_GET['TSOP'] == '1'){  echo 'checked="checked"';}?> /></td>
</tr>
<tr style="height: 21px;">
<td style="width: 25%; height: 21px;"></td>
<td style="width: 25%; height: 21px;"></td>
<td style="width: 25%; height: 21px;"> TSOP Typ 2</td>
<td style="width: 25%; height: 21px;"><input name="TSOP" id="TSOP" type="checkbox" value="2"<?php if($_GET['TSOP'] == '2'){  echo 'checked="checked"';}?> />     </td>

</tr>
<tr style="height: 21px;">
<td style="width: 25%; height: 21px;"></td>
<td style="width: 25%; height: 21px;"></td>
<td style="width: 25%; height: 21px;"> LGA</td>
<td style="width: 25%; height: 21px;"><input name="LGA" id="LGA" type="checkbox" value="1"<?php if($_GET['LGA'] == '1'){  echo 'checked="checked"';}?> />    </td>
</tr>

And here the PHP Part how i populate the Dropdown.

<td style="width: 14.2857%; height: 21px;">  <select id="FlashID" name="FlashID" onchange="FlashFunction()" size="1" >

                    <option disabled selected value> </option>;                             
            <?php
            foreach($connection->query($flash) as $m)
            {
                        if($m['FlashID'] == $_GET['FlashID']){
                $isSelected = 'selected="selected"';
            }else{
                $isSelected = '';
            }
            echo "<option data-COB='".$m['COB']."' data-SMT='".$m['SMT']."' data-BGA='".$m['BGA']."' data-TSOP='".$m['TSOP']."' data-LGA='".$m['LGA']."' value='" . $m['FlashID'] . "'".$isSelected."  >" .$m['SAP'] ."</option>";

            }
            ?> 
            </td>

Here is the SQL Table for the poplated Dropdown

FlashID   SAP   COB   SMT   BGA   TSOP    LGA
1        102292  0     1     0     2       0
3        102293  0     1     0     2       0
4        102294  0     1     0     2       0
5        102296  0     1     0     0       1
6        102412  0     1     0     1       0
7        102413  0     1     0     1       0
8        102414  0     1     0     1       0
9        102651  0     1     0     2       0
10       102652  0     1     0     2       0
11       102664  0     1     0     2       0

This is my not working Javascript Part:

<script>
function FlashFunction(){
var index = document.getElementById("FlashID").selectedIndex;
var COB = document.getElementById("FlashID").options[index].getAttribute("data-COB");
var SMT = document.getElementById("FlashID").options[index].getAttribute("data-SMT");
var BGA = document.getElementById("FlashID").options[index].getAttribute("data-BGA");
var TSOP = document.getElementById("FlashID").options[index].getAttribute("data-TSOP");
var LGA = document.getElementById("FlashID").options[index].getAttribute("data-LGA");
document.getElementsByName("COB")[0].value = COB;
document.getElementsByName("SMT")[0].value = SMT;
document.getElementsByName("BGA")[0].value = BGA;
document.getElementsByName("TSOP")[0].value = TSOP;
document.getElementsByName("LGA")[0].value = LGA;
}
</script>

Notice the TSOP can be value 1 or 2.

for ex. You see already if I select FlashID 6. TSOP and SMT Checkbox should be checked.

But atm I have no idea, how I can handle this in why my Javascript is not working Can someone help?