将Smartquotes转换为常规引号/注意：iconv（）：检测到输入字符串中的非法字符

My production server have iconv encoding set in php.ini as the following:

iconv.input_encoding    ISO-8859-1  ISO-8859-1
iconv.internal_encoding ISO-8859-1  ISO-8859-1
iconv.output_encoding   ISO-8859-1  ISO-8859-1

wheres

iconv.input_encoding    no value    no value
iconv.internal_encoding no value    no value
iconv.output_encoding   no value    no value

The issue is that on my production server Im unable to run my script which convert a string including some special characters to regular characters, in this case smart quotes to regular quotes. “test” to "test".

I tried this but didn't work. Can someone shed some light please. Thanks

 $output = iconv('UTF-8', 'ASCII//TRANSLIT', $input);
 $output = iconv('ISO-8859-1', 'UTF-8//TRANSLIT', $input);

I used mb_detect_encoding and detected input was ASCII. My server is set to ISO-8859-1.