Hello SteveMann, 6v6gt CrossRoads and the Arduino forum,
6v6gt:
You have currently 3 max7219 circuit boards. Any combination of two in a daisy chain works. Adding the third breaks it. Is that it ?
It seams unlikely that there is a hardware fault with the Arduino.
You now have to post a schematic and the full code.
This assessment is correct. Working on drawing schematic. Will post.
Allen