MCT Serial board mystery - Can you crack the pinout code?

[tony duell]

> 
> Decided to take a good shot at putting my only S-100 serial board to use.
> Figured the place to start was ID'ing the connector pin-outs so I could set
> up a cable and begin the process.
> 
> Lacking any docs whatsoever, all I could do was trace out the PCB and try
> to ascertain what was what. So here's what I've come up with - can +you+
> figure out which pin is which?
> 
> Board has two outputs, J1 & J2. They are standard 10-pin DIP headers, using
> the standard numbering scheme. We'll look at J1; J2 is essentially the
> same, but routes to different pins / chips / transistors.
> 
> Pin 1 - Col. of 2N3906 (Base is driven by opt. 2 of 1458 - see Pin 7)
> Pin 2 - Pin 28 (DB3) of both 1014 & 1015 UARTs
> Pin 3 - 1K pull-up to Vcc (12V? Same Vcc as 1458s)
> Pin 4 - 150R -> 47R -> Pin 6 w/ XNOR input 1A at 150/47 junction
> Pin 5 - n/c
> Pin 6 - 47R -> 150R -> Pin 4 w/ XNOR input 1A at 150/47 junction
> Pin 7 - 1K2 -> opt. 2 of 1458 (see Pin 1)
> Pin 8 - GND
> Pin 9 - 1458 opt. 1
> Pin 10 - GND

> So we have what looks like three (3) each Inputs & Outputs, plus a Vcc and
> GNDs:
> 
> Inputs - Pin 2, 4, 6
> Outputs - Pin 1, 7, 9
> Vcc - Pin 3
> Gnd - Pin 8, 10
> 
> So.. what do +you+ make of it? =)


Well...

First oddity is pin 2? What on earth is that for? Why bring out one data line with no enables, strobes, etc?
Are you sure about this?

Now, the 1458 is a dual op-amp. It was commonly used in old serial devices as a level shifter.

My guess is that pin 7 is an RS232-like voltage output, serial data. Pin i is a current loop output,
same data.

The receive input has me stumped at this point. I would guess it's pins 4 and 6. Again possibly current loop. 
I would trace out all the circuitry in that area. It is probably possible to connect it for RS232 input, but
no idea how without the complete circuit.

-tony