Consonant + chandrakkala in place of chillu

Following could be the reasons:

1. Your Malayalam Unicode font is an old version which does not follow the latest Unicode standard on Chillus. Please follow these instructions.
2. Your Windows PC does not have the latest Uniscribe DLL (usp10.dll). Please follow these instructions.
3. Your PC's operating system is older than Windows 2ooo.
4. You are using alternate browsers like FireFox whose ability to interact with Uniscribe is slightly limited compared to that of Internet Explorer.
   

Chillus in previous Unicode encoding standard can be converted to current standard using Varamozhi Editor. Convert old Unicode text to Manglish as described here. Then convert it to Unicode again by clicking File->Convert to Unicode(UTF8).