Invalid Character Data Problem

I am having some trouble pulling some data out from the database. I have
tried against both 7.4.5, 8.0b4 and 8.0b5 and get the same result.

I have used both the v308 and CVS HEAD of the JDBC driver.

When I SELECT from a certain table, I see this JDBC exception:

"Invalid character data was found. This is most likely caused by stored
data containing characters that are invalid for the character set the
database was created in. The most common example of this is storing 8bit
data in a SQL_ASCII database."

The database is indeed of type SQL_ASCII. The table stores mailing list data
and has about 400,000 rows.

Looking at the data via psql, I see that some of the rows have strange
characters in them, such as question marks where I would not expect them,
etc...

What are my options? Is there a way to identify the 'bad' records, or the
ones causing trouble?

Thanks,
Hunter