http://audio.manualsonline.com/manuals/mfg/pioneer/vsx819hk.htmlIt's in the manual. Page 12.
Resetting the Main Unit
Use this procedure to reset all the receiver's settings to the factory default. Use the front panel controls to do this.
1 Switch the receiver into standby.
2 While holding down the BAND button, press and hold the STANDBY/ON button for about two seconds.
3 When you see RESET? appear in the display, press AUTO SURROUND/STREAM DIRECT.
OK? shows in the display.
4 Press STEREO/A.L.C to confirm.
OK appears in the display to indicate that the receiver has been reset to the factory settings.