create table t (v text, ts tsvector);
create index t_ts_indx on t using gin (ts);

insert into t values ('XAS-5678');
insert into t values ('DAP-1230');
insert into t values ('DAP-12');
insert into t values ('DAP-123');
insert into t values ('DAP-12302356');
update t set ts = to_tsvector(v);

seb=# select * from t where ts @@ to_tsquery('DAP-1:*');
      v       |          ts
--------------+-----------------------
 DAP- 1230      | '-1230': 2  'dap': 1 
 DAP- 12        | '-12': 2  'dap': 1 
 DAP- 123       | '-123': 2  'dap': 1 
 DAP- 12302356  | '-12302356': 2  'dap': 1 
( 4  rows)

Time:  1 , 257  ms
seb=# select * from t where ts @@ to_tsquery('XAS:*');
    v     |        ts
----------+-------------------
 XAS- 5678  | '-5678': 2  'xas': 1 
( 1  row)

Time:  0 , 975  ms

seb=# \dF+ russian
Text search configuration "pg_catalog.russian"
Parser: "pg_catalog.default"
      Token      | Dictionaries
-----------------+--------------
 asciihword      | english_stem
 asciiword       | english_stem
 email           | simple
 file            | simple
 float           | simple
 host            | simple
 hword           | russian_stem
 hword_asciipart | english_stem
 hword_numpart   | simple
 hword_part      | russian_stem
 int             | simple
 numhword        | simple
 numword         | simple
 sfloat          | simple
 uint            | simple
 url             | simple
 url_path        | simple
 version         | simple
 word            | russian_stem

seb=# select version();
                                          version
-------------------------------------------------------------------------------------------
 PostgreSQL  9 . 0 . 1  on i686-pc-linux-gnu, compiled by GCC gcc (Debian  4 . 3 . 3 - 3 )  4 . 3 . 3 ,  32 -bit

select to_tsquery('DAP-1:*') ;
    to_tsquery
------------------
 'dap':* & '-1':*