If you use ng-model, you don't want to also use ng-checked. Instead just initialize the model variable to true. Normally you would do this in a controller that is managing your page (add one). In your fiddle I just did the initialization in an ng-init attribute for demonstration purposes.
<div ng-app="">
Send to Office: <input type="checkbox" ng-model="checked" ng-init="checked=true"><br/>
<select id="transferTo" ng-disabled="checked">
<option>Tech1</option>
<option>Tech2</option>
</select>
</div>