Flash ADC with TL074 & 74LS148: encoder inputs always high?
For 74LS logic, 1.4 volts is an "undefined" value.  An input must be below 0.8 volts to guarantee it will be accepted as a Low, and above 2.0 volts to be a guaranteed High.

The inputs will source 0.8 mA when taken low, so your op-amps must be able to sink that current while keeping their output voltage below 0.8 volts.