How to avoid error with convert() function

SELECT convert(myfield,'LATIN2','WIN1250') FROM tbl;

ERROR:  character 0x828e of encoding "MULE_INTERNAL" has no equivalent in
"WIN1250"

I know I have few characters like this one in table with about 1.000.000
rows.
How to avoid such error and show eg. ? instead of error , or how to replace
such characters with some normal chars ?

tnx