Based on your first email, the laser modules could light up with RS 485 connection, is this correct?
And you are trying to connect the SLD with parallel interface port but the laser module do not light up at all, is this correct?
If yes, in this case, it seems like the parallel interface board is faulty.
Is this faulty unit your “demo unit”?
Or it is from the customer?
If this is from the customer, can you share with me which customer?
It is for my record purpose only.
I remember you have 1 unit as demo.
And if these 2 units are in your office, you could try to check if the boards are “physically” the same?
If they are the same, you can swap the card and confirm.
If you replace the MCB, you might need to perform “measurement run” as shown in attached document (topic 3.3).
Hope the document will help and good luck!
If necessary, you may call me on my mobile phone +65 97239112 for further support on your troubleshooting.