SONY SLT-A77 ALPHA TRANSLUCENT MIRROR REPLACEMENT REPAIR DIY
This video shows how to replace the translucent mirror of Sony A77 camera, which had a mark on it. This mirror is used by other Sony models as well such as: SLT-A35, SLT-A57, SLT-A58, SLT-A65
You may order the translucent mirror here: