Hi,
Can you please post a copy of just how you connected the three digit display to the MAX7219 circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
You should be able to connect all the a segments together at the display board, same with b ,c ,d, e, f, g and dp.
So for a 3 digit display you should have 8 wires (segment) + 3 wires (commons anode or cathode) = 11 wires
Thanks.. Tom.. 