Put the receiver on a music channel and make sure you can hear it.
Then using the remote and pointing it at the receiver's IR sensor repeatedly
press or hold down the [GUIDE] button.
If the music goes out, i.e. the receiver displays the guide, you know
you still have a leak. Either reposition the mask or use some black
electrical tape to cover any problem areas. For receivers with the plexiglass
fronts see FAQ 8.