Mitsubishi MR-J2S Alarm AL.32 — What It Means and What It Costs to Fix
AL.32 is the MR-J2S overcurrent alarm, and on this family it overwhelmingly means one thing: the IPM — the intelligent power module — has failed. It is the classic J2S death, it is repairable, and the one thing you must NOT do is bolt a replacement amplifier onto an un-tested motor.
What's usually behind it
Failed IPM (the usual verdict)
The amplifier's intelligent power module shorts internally. The alarm appears instantly at enable, or the breaker trips at power-on. Repair replaces the IPM with a new module, verifies gate drive, recaps the bus, and powered-tests the amp — typically $450–$950.
Shorted motor or cable
A winding-to-winding or winding-to-ground short presents as amplifier overcurrent — and will destroy the next amplifier too. Megger the motor phases to ground before installing anything. Our free evaluation tests the amplifier independently, so if the amp is healthy you pay nothing and you've safely convicted the motor side.
Regeneration circuit faults (AL.30 family)
If you're seeing AL.30 rather than AL.32, the regeneration path (resistor or internal circuit) is the suspect — also a board-level repair.
Narrow it down yourself first
Work through these before you pull anything out of the panel. Several of them will tell you the unit is fine and the fault is somewhere else entirely.
- □Megger the motor and its cable before condemning the drive. A shorted winding or a cable chafed against the machine frame will destroy a replacement drive exactly as fast as it destroyed the first one.
- □Record the alarm code and what the machine was doing when it tripped — during acceleration, at speed, on a hard stop, or only when warm. That distinction separates a power-stage fault from a thermal or feedback fault.
- □Check whether the cooling fan still spins freely and whether the heatsink is clogged. If the only fault is a thermal trip, cleaning and a fan may fix it on your bench.
- □Confirm incoming line voltage and phase balance. Repeated drive failures on one axis are often a supply or wiring problem the drive is simply reporting.
- □Note your parameter set if you have it recorded. Drive parameters normally live in the CNC or the drive's protected storage and our physical repairs do not touch them, but a record is worth having.
What happens if you send it to us
If the checks above point at the unit, this is the sequence it goes through — the same one every time, so nothing gets skipped because a fault looked obvious.
- 1
Safe intake and bus discharge
Drives arrive holding charge in the DC bus capacitors. The unit is discharged and verified at zero before anything is opened — this is a genuine hazard on any drive with a large capacitor bank, not a formality.
- 2
Power stage integrity check
The IGBT or power module is checked device by device for shorted and open junctions before power is ever applied. Energising a drive with a shorted power module simply destroys more of it, so this is done cold, first, every time.
- 3
DC bus and pre-charge inspection
Bus capacitors are assessed for capacitance loss and elevated ESR, and the soft-charge circuit — inrush resistor and its bypass relay or contactor — is checked. A drive that reports undervoltage or trips on power-up very often has a failed pre-charge path rather than a failed power stage.
- 4
Gate drive and feedback circuitry
Gate driver stages and their isolation are tested, because a partially degraded driver produces asymmetric switching that reads as an intermittent overcurrent fault under load and as a perfectly healthy drive at idle. Encoder and feedback interfaces are checked for the damage a shorted motor cable pushes back into the drive.
- 5
Thermal path and cooling
Fans, heatsink airflow and thermal interfaces are serviced. A large share of "failed" drives are thermal alarms caused by a seized fan or a heatsink packed with production dust.
- 6
Powered test under load
The repaired drive is brought up through a controlled power-on and run against a load so the power stage, current regulation and thermal behaviour are proven in operation — not merely confirmed to power up without alarming.
Machine down? Let's get it back up.
Start a repair online in two minutes, or send us the part number for a free technician review.
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Call (817) 799-7332 · 📱 Text us a photo of your unit · Email repairs@controlboardlab.com