I want to change the character set of database. I did the following steps:

SQL> STARTUP MOUNT;
SQL> ALTER SYSTEM ENABLE RESTRICED SESSION;
SQL> ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0;
SQL> ALTER DATABASE OPEN;
SQL> ALTER DATABASE CHARACTER SET ;

But I got the error:

ORA-12716: Cannot ALTER DATABASE CHARACTER SET when CLOB data exists

Do I have to all columns with CLOB? Our schema does not use CLOB at all, so those CLOBs must be in the schema coming with 9i installation.
How can I find out where CLOBs are ?

Thanks for any help.