HEIDENHAIN iTNC 530 Service Manual page 246

for the axis to be traversed / the spindle to be rotated.
(A non-HEIDENHAIN inverter is probably also equipped with a corresponding LED or display.)
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Figure: Green LED READY UV on UVR 140 D (the green LED POWER MODULE READY
at top left must also be lit)
Check if the green READY LED lights up on, e.g.
the compact inverter
the UM axis module
the HEIDENHAIN interface board for the SIMODRIVE system
Figure: READY LEDs on a two-axis module
HEIDENHAIN Service Manual iTNC 530