Euchner MGB Gate Box — DIA/State LED Faults & Reset

Euchner · intermediate · 25 min

A Euchner MGB multifunctional gate box reports faults on two LEDs: red DIA means a fault, and the green State LED encodes the fault code. Learn to read the code against the system status table, tell latching from non-latching faults, and reset correctly.

ℹ️ On a Euchner MGB, the red DIA LED = a fault is present, and the green State LED encodes the fault code. Read the State code against the device's system status table, fix the cause, then reset — non-latching faults clear by re-closing the guard, latching ones need a proper reset.

Read the two LEDs

A Euchner MGB (Multifunctional Gate Box) shows its condition on two indicators, and reading them in order is the whole diagnosis:

  • Red DIA LED illuminated = a fault is present.
  • Green State LED = indicates the fault code (via its pattern/state).

You then match that State indication to the system status table in the MGB documentation for your exact variant. Importantly: if you can't find the displayed device status in the system status table, that itself indicates an internal device fault — the unit needs replacing/service.

Latching vs non-latching faults

The status tables distinguish fault types, and this decides how you clear them:

  • Non-latching faults can be reset by opening and closing the guard again — cycle the door and the MGB recovers on its own.
  • Latching faults use corresponding output bits to reset (via the control system), or require the reset input/button below.

Knowing which type you have stops you from power-cycling when a simple door cycle (or an output-bit reset) is what's needed.

How to reset

Besides switching the operating voltage off and on, the MGB gives you a dedicated reset:

  • Apply 24 V to the RST input for at least 3 seconds — this is the intended alternative to a full power cycle.
  • If the installation has a reset button, note it typically controls ALL integrated reset inputs in the series connection — so one button can reset several MGBs wired in series. Make sure that's the behaviour you expect before pressing it.

About the L1 / L2 variants

Guard-locking MGB variants differ in their locking logic, and the fault indication reflects it: for example MGB-L1 corresponds to no voltage at IMP, while MGB-L2 corresponds to voltage at IMP (the magnet/interlock input state). Use the status table for your variant so the code means what you think it means.

Step-by-step

  1. DIA red? A fault is present — read the green State LED code.
  2. Look it up in the system status table for your MGB variant. Not listed? Internal device fault → service/replace.
  3. Non-latching? Open and close the guard to clear it.
  4. Latching? Reset via the output bit from the controller, or apply 24 V to RST for ≥3 s (or use the series reset button).
  5. Re-validate the guard-locking/interlock function before returning the machine to service.

Never do this

Never bridge the RST input permanently or defeat the guard switch to stop a recurring MGB fault — the gate box is interlocking a hazard. Find the real cause (wiring, door alignment, the monitored contactor), reset by the proper method, and re-validate the safety function.

Key points

  • Red DIA LED = a fault is present; the green State LED encodes the fault code — read it against the MGB system status table for your variant.
  • If the displayed device status isn't in the system status table, that indicates an internal device fault (service/replace the unit).
  • Non-latching faults reset by opening and closing the guard again; latching faults reset via output bits from the controller or the reset input/button.
  • Reset by applying 24 V to the RST input for at least 3 seconds (the intended alternative to a power cycle); a series reset button resets all MGBs in the chain.
  • MGB-L1 = no voltage at IMP, MGB-L2 = voltage at IMP; never bridge RST or defeat the guard — fix the cause and re-validate the interlock.

Codes and symptoms

DIA (red) on — Fault present
The red DIA LED indicates a fault is present. Read the green State LED for the fault code and look it up in the MGB system status table for your variant.
State (green) code — Fault-code indicator
The green State LED encodes the fault. If the shown status isn't in the system status table, it indicates an internal device fault requiring service.
RST input reset — Clearing a latching fault
Apply 24 V to the RST input for at least 3 seconds as an alternative to a power cycle. A series reset button controls all integrated reset inputs in the chain.