PHP and SQL 2005 edit record JSON parse failed

I have this problem.. I want to edit a row using ajax to send data to SQL 2005 and the response is a JSON object with slashes. The jQuery Insert and delete good but when i use JSON for getting rows it doesn`t work

Here's the error:

Here's the PHP code: preins.php

 if(isset($_POST['editvalue']))
          {  
     $query_ed = "SELECT dbo.alumno.alumnoID, dbo.alumno.nombre, 
                         dbo.alumno.apaterno, dbo.alumno.amaterno,
                         CONVERT(VARCHAR, dbo.alumno.dateReg, 103) as dateReg, 
                         dbo.alumno.IDPeriodo
                   FROM   dbo.alumno
                   WHERE dbo.alumno.alumnoID= '{$_POST['id']}'";


              $sql_ed = sqlsrv_query($conn,$query_ed);
              if( $sql_ed === false ) {
             die( print_r( sqlsrv_errors(), true));
                                    }
              $obj_ed = sqlsrv_fetch_object($sql_ed);


          header("Content-type: text/x-json");
            // $obj_ed = stripslashes($obj_ed);
             //$obj_ed= mysql_real_escape_string($obj_ed);
             echo json_encode($obj_ed);
            // echo json_encode($obj_ed, JSON_UNESCAPED_SLASHES), "\n";  
              exit();
           }

Here's the AJAX:

jQuery(document).on("click", ".open-edit", function ()
 {
    jQuery('#save').hide();
    jQuery('#update').show();
    var IdEdit = jQuery(this).data('id');


     /*return false;*/
     jQuery.ajax({
                 url     : "preins.php",
                 type    : "POST",//url:'buscar.php?act=insertar',
                 datatype: "JSON",
                 data    : {
                                 editvalue : 1,
                                 id        : IdEdit
                                    },
                  success:function(show)
                               {
                 //   alert("Success AJAX: "+JSON.stringify(show)); // Read JSON
                  // jQuery('.modal-body #save').hide();
                     jQuery('.modal-body #update').show();
                     jQuery('.modal-body #txtida').attr('disabled',true);
                     jQuery('.modal-body #txtFecha_Pre_Inse').attr('disabled', true);
                     jQuery('.modal-body #txt_IDPeriodo').attr('disabled', true);


                     jQuery('.modal-body #id').val(show.alumnoID);
                     jQuery('.modal-body #txtida').val(show.alumnoID);
                     jQuery('.modal-body #txtnoma').val(show.nombre);
                     jQuery('.modal-body #txtapa').val(show.apaterno);
                     jQuery('.modal-body #txtama').val(show.amaterno);
                     jQuery('.modal-body #txtFecha_Pre_Inse').val(show.dateReg);
                     jQuery('.modal-body #txt_IDPeriodo').val(show.IDPeriodo);


                                },
            error: function(jqXHR, exception) {
               if (jqXHR.status === 0) {
                   alert('Not connect.\n Verify Network.');
               } else if (jqXHR.status == 404) {
                   alert('Requested page not found. [404]');
               } else if (jqXHR.status == 500) {
                   alert('Internal Server Error [500].');
               } else if (exception === 'parsererror') {
                alert('Requested JSON parse failed.');
               } else if (exception === 'timeout') {
                   alert('Time out error.');
               } else if (exception === 'abort') {
                   alert('Ajax request aborted.');
               } else {
                   alert('Uncaught Error.\n' + jqXHR.responseText);
               }
                                                              }
                     });
          //return false;                          
});