M91-t4-r6-zk1 Manual !!better!! -

A: Yes. During power-up, press and hold the "ESC" and "UP" buttons simultaneously for 5 seconds. Navigate to System > LCD Contrast.

| Error Code (LED Blink) | Root Cause | Solution from Manual | | :--- | :--- | :--- | | | Power supply below 19V | Check 24V DC regulator. Add capacitance. | | Solid Red (PWR LED on, RUN off) | Firmware corruption | Re-download OS via U90 (Section 5.4). | | Rapid Green/Red (Outputs frozen) | Watchdog timeout due to infinite loop | Review ladder logic for unconditional jumps. | | Y0 flashes, but no real relay click | Welded relay contact | Replace unit. Not field-repairable (r6 relays are sealed). | | RS485 comms fail (zk1 variant) | Termination resistor mismatch | Set DIP switch 4 to ON (120Ω term). | M91-t4-r6-zk1 Manual

A: No. The manual specifies that "zk1" units require a 2.5mm jack programming cable, not the older 3.5mm version. An adapter (part number: CAB-ZK1) is required. A: Yes