On a "normal" Burny 5 there is a input signal at 32 recp pin 11 and pin 24 that when high causes the machine to inhibit all movements.
Could be used on your machine to indicate that the torch is not in the top position, connected to the torch breakaway or any of many other causes.
Try following the cable.
On a Burny 5 without the 32recp on the back you must look into the drawings of the machine.