First thing, you are doing alpha conversion for a numeric field, which is wrong.
The field objek is of length 50 , which means it will add zeros till it become of same length.
It will not give any error but it will not give you the proper output.
In the if condition where you are doing conversion, try the method which I have suggested .
data lv_objek type objek.
lv_objek = l_i_mcha-cuobj_bm.
CALL FUNCTION 'CONVERSION_EXIT_ALPHA_INPUT'
EXPORTING
INPUT = lv_objek
IMPORTING
OUTPUT = lv_objek.
You might also get multiple values in l_i_mcha, so you need to put the working of if condition inside a loop. don't use select - endselect.
Not advised.