SQL & PL/SQL

Hi all
Im trying to load data into table that are in EBCDIC format.
Data is loaded into the table.
But some data in table are like small boxes and question marks.
Please advice me how to tackle this issue.

Please find the control file script that i used to load data.
------------------------------------------------------------------------------
LOAD DATA
CHARACTERSET WE8EBCDIC500
INFILE 'S:\IT\OPUS\D101011.PL.HXS.FILEOUTA.PRC475'
REPLACE
INTO TABLE test_sqldr_rajesh
(
C1 POSITION(1:80) CHAR nullif(6)='?'
, C2 POSITION(81:160) CHAR nullif(6)='?'
, C3 POSITION(161:240) CHAR nullif(6)='?'
, c4 position(241:320) CHAR nullif(6)='?'
, c5 position(321:400) CHAR nullif(6)='?'
, C6 POSITION(401:480) CHAR nullif(6)='?'
, C7 POSITION(481:560) CHAR nullif(6)='?'
, C8 POSITION(561:640) CHAR nullif(6)='?'
, C9 POSITION(641:720) CHAR nullif(6)='?'
, C10 POSITION(721:800) CHAR nullif(6)='?'
, C11 POSITION(801:880) CHAR nullif(6)='?'
)

Thanks
Jo