[GENERAL] Collate problem when using ORDER BY

Hi,

I'm new here. I work on a site that uses postgres version 8.1.5 and database encoding ISO_8859_8. When I sort select requests using order by the "weight" of the characters seem to be really funny (but consistent). It seems to me that if I create a "phantom" converted field such as:
SELECT field convert(field, "ISO_8859_8" ,"UTF8") as field_utf8 ORDER BY field_utf8;
Then the sort will be OK however, I get the error:
Query failed: ERROR: character 0xd7 of encoding "ISO_8859_8" has no equivalent in "UTF8".

Is it due to a "bad" character in the content?
Can I get rid of it like find/replace?
Can I change collate for a given table/database?

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