Onkyo TX-NR 838 Manual page 156

The display is dark
Make sure that Dimmer function is not working. Press DIMMER button
and change the brightness level of the display.
The following settings can be made for the composite video inputs
While holding down the input selector button to configure, press Home
once at a time until "Video ATT: On" appears on the display. To resume
the setup, repeat the above described step until "Video ATT: Off" appears
on the display.
This setting is possible for input selectors assigned with one of the video
inputs "VIDEO 1" to "VIDEO 3" in "1.Input/Output Assign" - "Composite
Video Input". If you have a game console connected to the composite
video input, and the picture is not very clear, you can attenuate the gain.
Video ATT: Off: (Default).
Video ATT: On: (Gain is reduced by 2 dB.)
The picture on your TV/monitor connected to the HDMI output(s) is
unstable
Try turning the DeepColor function off.
To turn off the DeepColor function, press STB/DVR and
on the AV receiver simultaneously.
While holding down STB/DVR, press
"Deep Color: Off" is appeared on the display. To reactivate the
DeepColor function, repeat the above described step until "Deep Color:
On" appears on the display.
ON/STANDBY repeatedly until
ON/STANDBY