PHP FPM returns HTTP 500 for all PHP errors
Try to find the following line in your php.ini:
display_errors = Offthen make it on
To post a more complete answer, I had used a production version of php.ini which has display_errors = Off. Instead of turning it on globally, what I do now is, for files which I need error reporting on, I use ini_set('display_errors', 'On'); at the beginning of the file.
Also I met the problem, and I set display_errors = Off in php.ini but it not works. Then I found the php[display_errors]=off in php-fpm.conf, and it will override the value of php.ini and it works.