As a learning experience, I am studying a 64K 80 COLUMN expansion card for the Apple IIe. The model number is 820-0067-D for those interested.
Anyway, I'm sure the schematic is online somewhere but I just wanted to do this for fun.
The first thing I noticed, however, is that it appears the designers used a Hex Schmitt Trigger Inverter (74LS14 PC) solely to enable another IC in the circuit (Octal Bus Transceiver SN74LS245N).
So on the 74LS14, they tied Y1 to !E on the 74LS245. And, since the 74LS14 has A1 tied to Y3 and A3 isn't connected to anything, it seems to enable the 74LS245.
Why would they do this? Why not just tie the 74LS245's !E enable pin to ground?
In fact, I can't see why the Schmitt Inverter is used at all. The only other connections it has is A6 to external pin 26 on the motherboard and Y6 tied to A5 and Y5 tied to nothing.
It just seems like a waste. Do you think it was used as some type of propagation delay? If so, seems like it would only be around 50ns or so.
Here is a crude schematic that I came up with. I might just try and dig up the real schematics to make sure I'm not crazy. lol
simulate this circuit – Schematic created using CircuitLab
EDIT
Looks like I was wrong. A3 does indeed connect to Y5. Also, A2 is not floating, it is connected to GND.
Best Answer
It seems your circuit is incomplete or got pins mixed up. It is extremely unlikely that outputs of the 74ls14 are used with the input being open.
Using a schmitt-trigger circuit when receiving clock/enable like signals to improve noise immunity is quite sensible. As the 74ls14 is inverting, connecting two inverters in series to remove inversion is sensible and common. Thus it seems like you miss the A3 input. Finally while the delay is small, it might be sensible to make sure that the clock or enable signal arrives after some data signal or further control pins. The propagation delay through two schmitt triggers might well be enough for that.