These older printers determine where the origin(s) are using limit switches. X min, X max, Y min, Y max, Z min, Z max. (Newer printers can detect the limits by measuring the current used by the stepper motors).
The output from my TAZ 6 with the nozzle in the center of the bed.
Send: M119
Recv: Reporting endstop status
Recv: x_min: open
Recv: x_max: open
Recv: y_min: open
Recv: y_max: open
Recv: z_min: open
Recv: z_max: open
Recv: z_probe: open
Recv: filament: TRIGGERED
Recv: ok P15 B4
If, for instance, the z_max switch is disconnected then the printer will keep raising Z until it jams itself against the top of the frame.
The output from my TAZ 6 when I attempt to move X, Y, and Z beyond their maximum limits
Send: G0 X300
Recv: ok P14 B4
Recv: echo:endstops hit: X:293.68
Send: G0 Y-20
Recv: ok P14 B4
Recv: echo:endstops hit: X:293.68 Y:-18.32
Send: G0 Z260
Recv: ok P14 B4
Recv: echo:endstops hit: X:293.68 Y:-18.32 Z:241.47
If your printer is close to your computer (or you have a helper), you don’t have to use gcode to move to the endstops, you can use your fingers to manually trigger the switches and check the output of M119.
You should be able to manually move the Z axis with the printer turned off. If you have dual Z axis stepper motors, you will need to move both of them the same number of turns. There is a procedure for leveling the X carriage but I don’t know the procedure for a Mini. You should be able to find it here by searching.
Once you have moved the Z axis away from the Z max switch, you can manually check that the printer controller board can see it open and close.
If the Z axis doesn’t move when you give it commands, then I believe there is a fuse on the controller board that may have blown because of too much current when the Z axis was jammed into the frame.