Enabling error displaying from PHP code doesn't work out for me. In my case, using NGINX and PHP-FMP, I track the log file using grep. For instance, I know the file name mycode.php causes the error 500, but don't know which line. From the console, I use this:
/var/log/php-fpm# cat www-error.log | grep mycode.php
And I have the output:
[04-Apr-2016 06:58:27] PHP Parse error: syntax error, unexpected ';' in /var/www/html/system/mycode.php on line 1458
This helps me find the line where I have the typo.