if the remove the BOB from the control box its possible to use the wires that are now connected to the E-stop switch
to make a temporary connection to a 12 to 24V power supply
see the red 2 pin connectors
as the BOB has a diode to prevent damage due to the reverse connection of the supply
you can power the board and when you get the polarity correct you will have 3 LED's on
one marked 24V that indicates the 10V regulator is working
the second you have the 5V supply to the 74HC245 IC's that buffer the 12 signals from the PC's printer port
the third LED indicates the relay controlled by pin 17 is on
all the BOB's inputs (pins 1 to 9 + 14 , 16 & 17) are pulled up to +5V by 10K resistors
all the 74HC245 outputs should be at +5V
so you should have + 5v on all the 3 pins of the connectors for the 5 axis ribbon cable connectors
assuming you put the D-type connector back together you can connect the multimeters negative wire to the HEX stud or the shell
to test the signal path for problem X axis
the 25 pin D-type connector on the BOB will be the mirror image (pins 13 & 25 on the right)
short pin 2 to ground (to the shell may be easier) and the3 pin ribbon cable connectors pin 2 should to down to 0V
short pin 3 to ground (to the shell may be easier) and the3 pin ribbon cable connectors pin 3 should to down to 0V
if you put some sleeving on the pins you not testing it will make it easier to avoid shorting the IC outputs
John