Background:
DX4WIN, like many other logging programs (eg. CT, NA, TR, WriteLog), toggles Pin 14 on the selected LPT port when the operator changes radios. The defacto standard is that Pin 14 is high when Radio 1 is selected. However, DX4WIN drives Pin 14 high when Radio 2 is selected. Although there are ways to reverse cables and the like, so that switching works properly, the LEDs on the DXD will always be reversed. The purpose of this modification is to rearrange the internal logic in the DXD, so that everything functions properly, and the LEDs truly reflect the selected radio.
Modification:
Inspection of the schematic shows that Pin 14 is routed to two different pins on the internal jumper block, P1. It goes to P1-Pin 1 through an inverter, and to P1-Pin 8 directly (not inverted).
The push-on jumpers provided with the DXD short adjacent pins, which is by design, since normally we want to connect P1-1 and P1-2, as well as P1-8 and P1-9. However, when using the DXD with DX4WIN, we want to reverse the inverted and non-inverted lines, that is, we want to connect P1-1 to P1-9, and P1-8 to P1-2. This will flip the logic, and result in normal behaviour with DX4WIN.
To accomplish this, we need a two conductor jumper cable with appropriate connectors on each end. The junk box at N3RD produced something useful, if not exactly correct. See the following photo.
Note that the cable has three wires, but only the white and black are being used. The red wire is on a pin that hangs over the edge of P1. You can clearly see that the white wire connects pins 2 and 8, while the black wire connects pins 1 and 9.
If neither your junk box (nor that of any of your friends) produces the needed cable, you can install jumper wires by carefully tack soldering them onto the sides of the appropriate pins. If you ever want to reverse the modification, be sure to clean all the solder off the pins using solder wick, so that the push on jumpers can be replaced.
Finally, Scotch Tape the provided blue push on jumpers onto the top of the circuit board, so that they don't get lost!