ABB IRB 6400R Product On-Line Manual page 336

Troubleshooting Tools
DIGIN1
26
Green Digital input. Lit when digital input is
active. The input is used for external start
signal/conveyor synchronization point.
If no light, faulty limit switch, photocell
etc. External wiring or connectors, short
circuit or broken wire. Faulty power supply
for input circuit (internal or external).
Defective input circuit on board.
Product Manual