RGB Video Output (PC Engine Duo-R)
It is common to install an 8-DIN Mega Drive 1 / Genesis 1 AV port on the PC Engine / Duo / Duo-R and use the additional 3 pins for RGB output.
You can use the existing composite video for SYNC or disconnect composite by cutting the trace to the composite pin, and wire from the HU6260 SNYC (pin 44).
The R (pin 49), G (pin 47) and B (pin 51) all come from the HU6260.
Notice the pinout of this mod uses different signals than the Master System 1 AV pinout, so you would want an RGB SCART cable wired correctly for this.
The RGB from the HU6260 isn't usable for most RGB monitors or receivers until you fix the DC offset, voltage level and impedance.
Passing the signals through a mod board such as the CleanRGB will give you perfect output signals you can run to the AV port.
The stock signals have a DC offset of 4V that needs to be removed, and an unterminated amplitude of 0.95V, instead of 1.4V, so a little dull.
Finally, the signals need 75R impedance on the end line for the AV port.
The CSYNC signal is also wrong. It has the same DC offset, but an unterminated amplitude of 0.95V instead of 600mV, so is too high.