Please take some photos of the PCBs so we know what version you have. Then I will post circuits if I have them.
I have never used with EMC2 so can't help with config needs. Only Mach3. Mach3 has many more features, I believe.
There is a varying frequency signal to the display board. With no signal it will show 80 when running.
It takes a tacho signal from the motor PCB.
If the display is blank, and all still works, then the display is most likely dead.
Be very careful around the front panel. TURN POWER OFF, and lower quill so the vernier does not damage the PCB when removing front panel.
Any shorts to chassis will almost certainly kill some/all PCBs!!