Array or not Array?

If I have a table as follows:

 

CREATE TABLE test1 (a char(5));

 

how would I test that the 2nd character of column a is NOT the letter 'b' for example.

 

In Informix I would say:

 

SELECT count(*) FROM test1 where a[2] <> 'b';

 

In POSTGRES I get an error saying "ERROR:  cannot subscript type character because it is not an array". I understand why I'm getting the error,  but I'm not sure how I do what I want to do?

 

Thanks to all in advance.

Atif