The Mitsubishi FR-A800 and FR-F800 share one platform. The FR-A800 is the high-performance general-purpose drive used on cranes, lifts, extruders and machine tools; the FR-F800 is the fan-and-pump version, adding optimum excitation control and dedicated PID functions for HVAC and water duties. Both display the same E.xxx fault family, store the last eight faults and share the option and parameter structure — so one troubleshooting workflow covers either model.
Knowing which codes point at the machine and which point at the inverter is what separates a one-hour repair from an unnecessary drive swap. Replacement VFDs and matching Mitsubishi spares are in our inverter collection; machine-tool retrofits that also need the motion side pair well with the Mitsubishi MR-J4-20A servo amplifier ($357.49) and the Mitsubishi HC-KFS43 servo motor ($114.14).
The FR-DU08 panel shows the fault as E.xxx with HOLD lit, confirming the output has stopped; the FR-LU08 LCD carries the same data with more text. Record three things first:
Warnings such as OL, oL, TH, FN and RB do not stop the drive; E.xxx faults do.
Fault manifestations. Output current reaches roughly 235 % of the inverter’s rated current and the output is cut. The suffix tells you when: OC1 during acceleration, OC2 at constant speed, OC3 during deceleration or stop. Expect a loud hum, a jerk, or a motor that never reaches speed.
Root causes. A ramp too short for the load; an output short circuit or earth fault; Pr.3 left at 60 Hz on a 50 Hz motor; Pr.19 not set to the motor rating; stall prevention set too high or the fast-response current limit disabled; a jammed load or a brake that does not release; encoder or U/V/W wiring errors under vector control.
Repair steps. Note the suffix and check the history for a repeating pattern. Lock out, megger the motor windings and cable to earth, then turn the shaft by hand — a seized bearing or a closed brake produces an overcurrent no parameter change will fix. If the mechanics are free, lengthen Pr.7 and Pr.8, lower the stall prevention level, enable the fast-response current limit and set Pr.3 and Pr.19 to nameplate values. If E.OC1 appears at every start, disconnect the motor and restart: persisting with no load means the output stage has failed.
Fault manifestations. Regenerative energy pushes the DC bus above the trip level during acceleration (OV1), constant speed (OV2) or deceleration (OV3). OV3 on a fast stop is the classic case; OV1 shows up on downward travel of vertical loads.
Root causes. Deceleration too short for the load inertia; supply over-voltage or a surge; no braking resistor where the application needs one; Pr.22 set below the no-load current; acceleration too slow in a lift application.
Repair steps. Measure the three-phase input and confirm it is inside the drive rating, then lengthen the deceleration time to match the load inertia. Enable the regeneration avoidance function (Pr.882 to Pr.886), set Pr.154 to 10 or 11 and set Pr.22 above the motor no-load current. On high-inertia or overhauling loads, fit a braking resistor, brake unit or an FR-CV regeneration converter — parameters alone cannot absorb continuous regenerated energy.
Fault manifestations. The output is cut when the supply falls below roughly 300 V AC on a 400 V class drive (150 V AC on 200 V class), or after a very brief supply interruption.
Root causes. Voltage sag from a large motor starting on the same line; the P/+–P1 jumper missing, or removed for a DC reactor and never refitted; input phase loss or a blown fuse; ageing DC bus capacitors.
Repair steps. Measure all three line-to-line voltages under load and watch for dips when other loads start, then verify the jumper and check input fuses and contactors. If the supply is healthy and the fault persists, the rectifier or bus capacitors are suspect — replace the drive.
E.THT (H30) — inverter overload. The drive has run at or above rated output current long enough for the module temperature to reach the protection level (150 % for 60 s). Check the acceleration/deceleration times, torque boost, load pattern selection and whether the machine is simply overloaded.
E.THM (H31) — motor overload. The electronic thermal relay has tripped on the motor. Verify Pr.9 against the nameplate full-load current and check that Pr.71 is set for the motor actually fitted — a constant-torque motor must be declared as such. Motors running below 30 Hz lose their own cooling, so add forced ventilation rather than raising the trip threshold.
E.FIN (H40) — heatsink overheat. Ambient above specification, fins clogged with dust or fibre, or a stopped cooling fan. FN normally appears before the trip, so treat FN as a service call. Clean the fins with dry compressed air, confirm the fan turns freely and fix cabinet airflow.
E.OLT (H60) — stall prevention stop. Under V/F control the output frequency has been pulled down to 0.5 Hz and held for three seconds; under vector or PM sensorless control it has dropped to the Pr.865 level with torque above Pr.874 for the same period. Reduce the load, then set Pr.22, Pr.865 and Pr.874 correctly.
E.GF means earth-fault overcurrent on the load side; E.LF means one of U, V or W is open. Disconnect the motor at the drive, megger each phase to earth (below 1 MΩ is a fault), then repeat at the motor end to separate cable from winding. Look for cable crushed in conduit, oil-soaked insulation and moisture in the terminal box. Never keep resetting an earth-fault trip — repeated attempts take the IGBTs with them.
| Interval | Task | Acceptance criterion |
|---|---|---|
| Weekly | Listen to the cooling fan; check for FN alarms; compare load current with nameplate | Fan quiet; current within rating |
| 6 months | Clean heatsink fins and cabinet filters; check terminal torque | No dust bridging; terminals tight |
| Annually | Megger motor and cable; review the fault history; back up parameters | Above 100 MΩ; backup stored off-machine |
| 3–5 years | Replace the cooling fan; inspect DC bus capacitors | Fan free-running; no bulging or leakage |
Keep one identical drive and a set of cooling fans on the shelf. Fans and clogged heatsinks cause most unplanned FR-A800/FR-F800 downtime, and both cost far less than an emergency replacement.
Do the FR-A800 and FR-F800 use the same fault codes?
Yes — the fault list and data codes are common to the platform; the differences are in control functions, not diagnostics.
Can I reset and restart after E.OC1?
Find the cause first. A reset with the same short circuit or jammed load trips again, and repeated trips stress the output stage.
The cooling fan runs but I still get E.FIN. Why?
Check the heatsink fins and cabinet — a fan that spins but cannot move air, with clogged fins or blocked filters, produces the same trip.
How do I know whether the fault happened during acceleration or deceleration?
Read the fault history. The panel may show only the latest code, but each record carries its data code (H10/H11/H12 for the three overcurrent cases).
Mitsubishi, FR-A800, FR-F800 and FR-DU08 are trademarks of Mitsubishi Electric Corporation. Always work from the FR-A800/FR-F800 Instruction Manual (Detailed) for your model.
By Jennifer Zhang — Test Well Electronics supplies tested Mitsubishi inverters, servo drives, motors and other industrial automation spare parts worldwide.
