No picture from monitor out on Onkyo TX-DS898
I realize you may have already doubled checked but make sure you follow this from the manual:
If the satellite tuner / cable box is equipped with an S video output
terminal, connect it to the S VIDEO 3 (or 4) IN terminal with an S
video cable. If it does not have an S video output terminal, connect
its video output terminal to the VIDEO 3 (or 4) IN terminal using an
RCA-type video connection cable. You do not need to connect to
both the S VIDEO 3 (or 4) IN and VIDEO 3 (or 4) IN terminals. If
the satellite tuner or television has component video outputs,
connect them to one of the COMPONENT VIDEO INPUT jacks.
With the initial settings of the TX-DS898, the VIDEO 3 and
VIDEO 4 input sources are set for the COMPONENT VIDEO
INPUT 2 jack.
If the video connection is made at COMPONENT VIDEO INPUT
1, this must be changed at the Setup menu: Input Setup → Video
Setup → Component Video (see page 35).
Using an RCA-type audio connection cable, connect the audio
output terminal on the satellite tuner or television to the same
VIDEO 3 (or 4) IN audio jacks on the TX-DS898. Make sure that
you properly connect the left channel to the L jack and the right
channel to the R jack.
If the device has a digital output jack as well, be sure to also connect
it to either a DIGITAL INPUT (COAXIAL) or DIGITAL INPUT
(OPTICAL) jack on the TX-DS898 depending on the device.
With the initial settings of the TX-DS898, the VIDEO 3 input source
is set for digital input at the OPTICAL 3 jack, and the VIDEO 4
input source is set for digital input at the OPTICAL 4 jack.
If the digital connection is made at a different jack, this must be changed
at the Setup menu: Input Setup → Digital Setup (see page 33).