The published diagrams for a modification required on a Gotek when used with the IBM 3174 shows the double row header (2 x 7) for customization, with the pairs labeled J5, JA, JC, JB, S0, S1 and M0 from left to right on the board and top to bottom in the diagram below.
Based on this, I assumed that the numbering of the pins on the Gotek header had 1 at the upper left and 14 at the lower right. That matches the diagram if you rotate it:
Based on this, I soldered the diode to the top left pin and the other side across the bottom. The Gotek has no numbers on the silkscreen for the header on either side of the PCB, but the assignment of the pairs of pins matches the diagrams nicely.
MY DISCOVERY
I discovered that in fact the diagram is flipped compared to the header strip! I decided to beep out the header pin connections to various IDC connector pins and VSS, which proved that the correct numbering of the header block should have pin 1 at the bottom left and pin 14 at the upper right.
The diode is intended to pull pin 4 down to ground as the Select Drive 1 pin is pulled to ground by the 3174. This tells the 3174 that the drive is ready with a diskette installed, once the 3174 selects the drive for use. As it was erroneously placed, it was reversed in polarity between the Select pin and ground, therefore doing absolutely nothing.
CORRECTION AND TEST
I removed the diode from the incorrect position and soldered it to the proper pins. With that in place, I put the drive back into the 3174 and attempted the IML again. It worked perfectly!
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