What precisely do you mean by "two identical signals"?
Where did these "two identical signals" come from?
How do you know that they are "identical"?
What happens if you REALLY input exactly the ONE SAME signal into both the inverting and non-inverting input?
That is the only way you will genuinely have "two identical signals".
Furthermore, if you seek complete perfect cancellation of the inverting and non-inverting signals, you will need to precisely match the value of the resistors. Have you done that? What is the actual measured value of all the resistors?
When I look at the "Simplified Schematic" diagram on page 8, it appears that if you ground the "null pins" (assumed to be pin 1 and pin 8?), it will render the input stage of your op-amp inoperable, so it is a wonder that you are getting anything form the output.
Thank you for taking the time to reply.
These signals come from a SDG2042X dual output AWG. Before the signals go to the breadboard I check to make sure they are at the same phase and Vpp on the oscilliscope, but that is done via BNC. I just checked on the breadboard with some probes just to make sure. It appears the voltage to the non-inverting input is slightly less. Using the same signal on both inputs yields the same result.
Without a proper power supply, I think it might be hard to find the resistance of each resistor, but I can attempt this. Perhaps I can find a battery laying around.
Perhaps I had the setup wrong when I grounded both nulls. I just set up everything on the breadboard again.
If what I am seeing on +IN and -IN is true, then the difference being displayed on my oscilloscope it wrong. So I'm a bit at a loss.