JavaScript - uncheck radio button if no checkboxes are checked

I already asked a different question here: JavaScript - Select radio button if any checkbox is checked

I had another question so I am creating a new question for this. I was told to do the same. Hence, the new question. Hope it's alright.

I'm able to populate the radio button Radio 1 if any PD checkbox in Groups 1 and 2 are checked. Similarly, I'm also able to populate the radio button Radio 2 if any ID checkbox in Groups 1 and 2 are checked.

Following is the HTML:

<form>
   <h3>Radio Buttons</h3>
   <input type="radio" name="radio1" id="radio1"> Radio 1
   <br>
   <input type="radio" name="radio2" id="radio2">Radio 2
   <br>
   <br>

   <h3>Checkbox Groups</h3>

   <h4><u>Group 1</u></h4>
   <p align="center"><u>PD</u></p>
   <ul>
      <li>
          <input class="pdcb" type="checkbox" name="G1PD1" onclick="validate()">G1 PD1</li>
      <li>
         <input class="pdcb" type="checkbox" name="G1PD2" onclick="validate()">G1 PD2</li>
   </ul>
   <p align="center"><u>ID</u></p>
   <ul>
      <li>
         <input class="idcb" type="checkbox" name="G1ID1" onclick="validate()">G1 ID1</li>
      <li>
         <input class="idcb" type="checkbox" name="G1ID2" onclick="validate()">G1 ID2</li>
   </ul>

   <h4><u>Group 2</u></h4>
   <p align="center"><u>PD</u></p>
   <ul>
      <li>
     <input class="pdcb" type="checkbox" name="G2PD1" onclick="validate()">G2 PD1</li>
      <li>
         <input class="pdcb" type="checkbox" name="G2PD2" onclick="validate()">G2 PD2</li>
   </ul>
   <p align="center"><u>ID</u></p>
   <ul>
       <li>
          <input class="idcb" type="checkbox" name="G2ID1" onclick="validate()">G2 ID1</li>
      <li>
          <input class="idcb" type="checkbox" name="G2ID2" onclick="validate()">G2 ID2</li>
   </ul>
</form>

Following is the JS code:

function validate()
{
var pdcbClass = document.getElementsByClassName("pdcb");
var idcbClass = document.getElementsByClassName("idcb");
console.log(this);

for (var i = 0; i < pdcbClass.length; i++) 
{
    if (pdcbClass[i].checked == true) 
    {
        document.getElementById("radio1").checked = true;
        document.getElementById("radio2").checked = false;
    }
}

for (var i = 0; i < idcbClass.length; i++) 
{
    if (idcbClass[i].checked == true) 
    {
        document.getElementById("radio1").checked = false;
        document.getElementById("radio2").checked = true;
    }
}

var pdcbClass2 = document.getElementsByClassName("pdcb");
var idcbClass2 = document.getElementsByClassName("idcb");
console.log(this);

//if none of the checkboxes are checked, don't populate radio buttons
for (var i = 0; i < pdcbClass2.length; i++) 
{
    if (pdcbClass2[i].checked == false) 
    {
        document.getElementById("radio1").checked = false;
        document.getElementById("radio2").checked = false;
    }
}

for (var i = 0; i < idcbClass2.length; i++) 
{
    if (idcbClass2[i].checked == false) 
    {
        document.getElementById("radio1").checked = false;
        document.getElementById("radio2").checked = false;
    }
}
}

Now, my question is how would I get the radio buttons to not get populated if none of the checkboxes are checked?

PS: I need to write this in pure JavaScript. I cannot use jQuery.