Vivitek RP56HD21-A - Manual (Page 48)

You can see a picture but you cannot hear sound
Make sure that the volume is not turned down.
Make sure that the sound is not muted.
Make sure that the internal speakers are turned on.
Make sure that your audio input source cables are connected securely and
correctly.
The monitor has pixels that are always dark
Your RPTV is manufactured using an extremely high level of precision
technology. However, sometimes some pixels of your RPTV may not
display. Pixel defects within industry specifications are inherent to this type
of product and do not constitute a defective product..
You see “noise” or “trash” on the screen
When your RPTV’s digital capabilities exceed a digital broadcast signal, the
signal is up-converted (increased) to match your RPTV’s display capabilities.
Up-converting can cause noise or trash.
Screen brightness is diminished
Video display devices experience degradation of brightness over the life of
the device. Normal brightness degradation is not covered by your warranty.