Mitsubishi MELFA CR750 — Error Levels & Reset Recovery

Mitsubishi · beginner · 20 min

MELFA robot errors carry a level prefix (H, L, C) that tells you how to recover. Learn which errors clear with the ERROR RESET button and which require a controller power cycle.

ℹ️ The letter in front of a MELFA error number is the most useful character on the screen — it tells you the severity and how the error can be cleared before you read anything else.

Read the level prefix first

On a Mitsubishi MELFA CR750 / CR751 controller, every error is shown with a number and a level prefix letter that defines its severity and how it clears:

• H (High) — serious error. The servo is turned off and the robot stops. Many high-level errors cannot be cleared by ERROR RESET alone; you must correct the cause and cycle controller power OFF then ON.
• L (Low) — less serious. The servo turns off and the robot stops, but the error can usually be cleared with the ERROR RESET operation once the cause is gone.
• C (Caution) — warning only. Operation is not stopped; the message informs you of a condition to review.

So before anything else, look at the letter: H means "fix it and power-cycle," L means "fix it and ERROR RESET," C means "note it."

Step-by-step recovery

1. Record the full code. Note the complete error number with its prefix from the teaching pendant (R32TB / R33TB) or from the controller display. In RT ToolBox3 you can open the error history and read the description, cause, and recovery for that exact number — this is the authoritative source.
2. Clear the physical cause. Depending on the error: release a pressed emergency stop, close an open safety gate, clear an interference/position problem, or resolve an overload (check payload, speed, and mechanical binding). The robot will not stay reset until the cause is gone.
3. Reset the error.

• For L-level errors: press ERROR RESET on the teaching pendant (or the controller). The error clears if its cause has been removed.
• For H-level errors: after correcting the cause, turn the controller power OFF, wait, then ON. Some high-level and duplex/safety errors are designed to require a power cycle so a serious fault can't simply be reset away.

1. Turn the servo back on. With the error cleared, enable the servo (SERVO ON) from the teaching pendant or your operation panel. Confirm the servo-on lamp/state.
2. Recover position if needed. If the stop left the robot off-path, use RT ToolBox3's position-recovery assistance or jog carefully in a manual mode back to a safe start position before resuming the program.

Origin / home not set

After certain maintenance or an encoder/battery event you may see an origin-not-set condition. In that case the robot cannot run programs until the origin (home) position is re-established using the documented origin-setting method for your model (data input, mechanical stopper, or jig method) in RT ToolBox3.

Good practice

Keep RT ToolBox3 connected during commissioning and maintenance — its error history and per-code cause/recovery text turn a bare number into a specific action, and its position-recovery function shortens downtime after a stop.