Well done on your retrofit. I am trying to convert a Leadwell lathe using the SZGH control. I also need to convert my turret signals from PNP to NPN. I have a ULN2803a Chip and also a complete board with the chip. In the SZGH manual, they are very clear that we do not supply 24v to the inputs on the control. When playing with the board on the bench I always have the ULN2803a chip go high to 24v when not taking the input to 0v. Did you also have this issue? Would it be possible to send me your circuit diagram of the converter you used? Thanks