This is typically how a healthy input would looks like. Sometimes, it can be a bit different, but the important factor is the transition over the (gray area) restricted band.
The signal must go through the gray area (which is standard TTL-restricted range 0.8V-2.2V) in order to sense the change. The signal must not stay in the gray area.
Take a look and compare in order to determine if the inputs are ok or not.