Custom post type query by metabox value

I've created a custom post type for "portfolio" with a custom metabox with a lot of extra fields, one of which is a checkbox that I'm using to determine whether this post type contains a case study, but I've hit a snag and I can't see where I've gone wrong. The output for the checkbox is either 'yes' or ''.

The setup in my metabox build is:

<input type="checkbox" name="rccustom_fields[case_study]" value="yes" <?php if ( isset($meta['case_study']) && $meta['case_study'] === 'yes' ) echo 'checked'; ?>>

And I can see the values exist as expected by outputting:

$meta = get_post_meta( $post->ID, 'rccustom_fields', true );
 print_r($meta);

BUT, when I pull a basic WP query with args to filter those results:

$args = array(
'numberposts'   => -1,
'post_type'     => 'portfolio',
'meta_key'      => 'case_study',
'meta_value'    => 'yes',

I get nothing returned, even though doing the print_r shows me that the meta value does indeed exist and is equal to 'yes'. (if I comment out the meta_key/meta_value lines, all posts from the custom post type do display)

Anybody see something I don't here?

Try below code , It may help to you.

$args_portfolio = array (
    'post_type' => 'portfolio',
    'posts_per_page' => -1,
    'post_status' => 'publish',
    'meta_query' => array(
        array(
            'key' => 'case_study',
            'value' => 'yes',
            'compare' => '=',
        ),
    ),
);

$data_portfolio = new WP_Query( $args_portfolio );