The boards came in from OSH Park, and I’ve compared the OEM cable to the cable built with my PCB.
I found an OEM cable for a brother FB100 portable disk drive on ebay, and split it in half to make two of the cables. The third one, I used the flat cable from A Cisco serial cable, and modified a 16 pin PCB mount header connecter to use just the inside 8 pins with the key.
I purchased 3 DB25 Male connectors with shrouds for the computer end.
Here’s what the stages looked like soldering the PCB.
After I assembled my cable, I checked the through connections checking for continuity and shorts. All checked good. I then checked the 3 paths that have the transistors to compare them to the OEM cable I have. The results are shown below.
The upper 3 Images are of the OEM cable and the bottom 3 are my cable. The newer transistors have a slightly higher gain with a little lower forward voltage. When connected, my cable behaves just like the OEM.
The only issue I had was with my model 100. The opening for the DB25 is too narrow for the shroud on the connector I purchased to fit into easily. The Model 102 has more clearance around the DB25 and the cable fits easily.
Here’s a closeup of one of the transistors and the reason I think this might be Marty’s mysterious device.
As you can see, it is clearly marked “14” just as Marty said the devices he found were.
I know this might be re-inventing the wheel, but just thought I’d toss my idea in the mix.