Single unrecognized character wrecks entire display

[Alexandre Oberlin]

Hi all,

I have a file created by a translation software. The file initially
displayed well in emacs and after some edit in the translation software it
didn’t anymore and reverted to raw text. I got this message when I tried
to save in utf-8:
   utf-8-mac cannot encode these: \351 \350 \351 \342 \351 \234 \350 \350
\311 \240

In short all the non ASCI had become unrecognized. However once I removed
a \234 character,that should display as œ, I could save it and recover a
correct display in emacs.

Is there a way to quickly spot the offending character within emacs in
such cases ?

Alexandre