Recently purchased the above mentioned 2 Channel high power relay for use with a RPI 3. Installed everything per the Github repository for Raspberry Pi, but i2cdetect -r -y 1 does not detect the relay board. I have verified the 12VDC input and have tried various jumper combinations all with no luck. Using the NCD “Screw Terminal Breakout Board with I2C for Raspberry Pi Zero, Pi 2, or Pi 3” for the i2c connection. I have updated /etc/modules and /boot/config.txt and they seem to have the correct info.
one more things you can check is the ribbon cable between pi and the i2c shield.
make sure the cable is properly connected and its connected to the black connector on both sides.
if cable is not locked properly it might cause this kind of issue.
this is what i will do
unplug the cable and inspect visually and make sure the ribbon cable is making proper connections with black connectors.