For those who can´t use mb_convert_encoding() to convert from one charset to another as a metter of lower version of php, try iconv().
I had this problem converting to japanese charset:
$txt=mb_convert_encoding($txt,'SJIS',$this->encode);
And I could fix it by using this:
$txt = iconv('UTF-8', 'SJIS', $txt);
Maybe it´s helpfull for someone else! ;)