decode error 500

[beetea2]

On my local test site I am locked out of both the front end and the back end with error 500.

How can I turn on error reporting? Or otherwise decode the encrypted error message?

In php.ini I set

display_errors = on

I added 

ini_set('display_errors', '1');
ini_set('display_startup_errors', '1');
error_reporting(E_ALL);

to config/config.inc.php

What else can I try?

[beetea2]

I got it: set config/defines_custom.inc.php

define('_PS_MODE_DEV_', true);