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

[Tothwolf]

On Fri, 14 Nov 2014, drlegendre . wrote:

> 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? =)

Standard numbering scheme? Surely you jest? ;)

Do you mean something like this?

2 4 6 8 10
. . . . .
. . . . .
1 3 5 7 9

It sounds like you've just about got it figured out though. If you have 
the datasheet for the 1458 (aren't there 1459s on the board too?) then you 
can follow the signals through the level converters back to the UART, and 
its datasheet should then tell you exactly which signals are which.

It makes sense that pin 10 would be an extra ground too, since it is quite 
possible they originally used a 9-conductor ribbon cable and wouldn't have 
connected that pin. You may also find than the signals come out on the 
correct pins of a DE9 connected to a 10-pin IDS connector with some 
9-conductor ribbon cable.