What are these mods for?

[dave]

If you are able to trace out the circuit, it will be easier to guess the purpose. For example, the 7475 chips are either latching data from the address bus for output, or sampling the ports for the address bus. The 7402 is likely for address and r/w decoding. I would guess each latch has 4 pins to the data bus and 4 or 8 pins to the port, but which pins are connected to the port vs the data bus would tell us if this is an input port, an output port, or a few bits of each.

If the at least some of the latch outputs are on the data bus, then I would guess this is a joystick or keypad interface. If all the outputs are on the port, then I might guess it's a parallel output such as a centronics interface. Of course, being right next to the keyboard, a joystick or keypad interface would seem like a good guess. Or a controller for a lost custom peripheral, such as a sound board.

[Klyball]

it looks to me like the connector goes both to the input and output of the latches , no data or address lines , the only thing going to the connector is the keyboard lines, but hard to say with out a drawing.

[dave]

Wow, I didn't even see the pic of the back of the board. It sure doesn't look like any address or data lines are hooked up.

I wonder what's driving the enable lines. I am having a hard time following the rats nest in the photo. Is it possible to trace this out and figure out

1) f anything other than the connector is connected to an input or output of either latch
2) what is driving the enable signal. If it's an otherwise unused gate, or a gate from the 7402 in the first prototype footprint, then try to figure out what that is wired to.