I wanted to replicate a comparator circuit to PCB and I later noticed that I mistakenly swapped the inverting and non-inverting inputs. The comparator used is LM2903. Surprisingly the board was still outputting normal besides with a lot of noise in rising and falling edges. The complete initial working circuit on a euroboard is as shown in below schematics:
To make the question more clear I simplified the original board as following:
And here its plots:
The thing is the above LTspice simulations do not show big differences. But for the PCB version(inputs swapped version) when I check the rising and falling edges with a scope I see something like in below hand drawn plot:
It is like some oscillation is superimposed only during rising and falling edges.
Should I definitely swap back the inputs? Can the nosiy rising and falling edges be the result of such swapped inputs?
I swapped back to the original one and the issue disparaged. It was not easy to do on the PCB though it look ugly: