He replaced the relay. The green light on the FANUC CPU blinked. On the pendant, Rung 214’s virtual current flowed again, a digital river crossing a logical gate.
“But the alarm is here,” Arjun murmured. He stopped on Rung 214. It was a simple seal-in circuit. A start button (X1.0) that latched a motor contactor (M10). But the contactor’s auxiliary contact (M10a) wasn’t sealing.
“Start the cycle,” Arjun said.
“See this rung?” Arjun pointed. “X3.0 is the left safety gate. X3.1 is the right safety gate. Y2.4 is the ‘Gate Closed’ relay. The logic says: If X3.0 AND X3.1 are true, then energize Y2.4.”
“The weld has cracked,” Arjun said. “The relay feels closed, but the ladder knows the truth. The current flows up to the gate, then… nothing. A broken bridge.” fanuc ladder
He navigated to the diagnostics. The screen displayed a grid of contacts and coils.
