All checkboxes checked at tableselect form

I have a Drupal form, with a tableselect element:

$form['items'] = array(
          '#type' => 'tableselect',
          '#prefix' => '<div id="wrapper-i">',
          '#suffix' => '</div>',
          '#header' => $header,
          '#options' => _ajax_items_options($selected),
          '#multiple' => TRUE,
    
          '#empty' => t('No hay elementos para ingresar'),
        );

I need all items are checked initially. This Items change through ajax in function of a previous select element form:

$form['entidad'] = array(
      '#type' => 'select',
      '#title' => t('Selecciona'),
    
     
      '#options' => $entidades,
      '#description' => t('Formas disponibles'),
     '#ajax' => array(
         
          // 'event' => 'change',
          'callback' => 'ajax_items_callback',
          'wrapper' => 'wrapper-i',
          'effect' => 'slide',
        ),
    ); 

How I can check all items at tableselect element?

At tableselect element I added:

'#default_value' => _ajax_items_options_check($selected)

_ajax_items_options_checks returns a array like this
$check[1]=true
$check[2]=true

The first time all items are checked, but when I change select element, with ajax, the tableselect form element will change your data but not refresh #default_value and items are not checked.

What am I doing wrong?