Mitsubishi Electric
Mitsubishi Servo Amplifier Repair (MR-J2S / MR-J3 / MR-J4, MDS) — Mail-In
Component-level repair for Mitsubishi servo amplifiers: the massive MR-J2S installed base plus MR-J3, MR-J4, and MDS CNC drives. Free evaluation, firm quote, typical repairs $450–$950.
Coverage: MR-J2S (10A–700A, A & B) · MR-J2 · MR-J3 · MR-J4 · MDS series CNC drives
✓Fixed — or it's free
Unrepairable units are refunded; evaluations cost $0
✓24-month warranty
Every repair covered, parts and labor
✓3–5 business days bench time
Rush (1–2 day) and emergency service available
✓Program preserved
Your application and settings stay in the unit
Symptoms this repair fixes
- ✓AL.32 / overcurrent class alarms
- ✓AL.10 undervoltage, AL.30 regeneration faults
- ✓Dead amplifier — no display
- ✓Trips breaker at power-on
- ✓Encoder communication alarms traced to the amp
Honest limits
- ✕Motor and encoder failures (identified at evaluation before you spend anything)
What you get
- ▸Free bench evaluation and firm quote
- ▸IPM (intelligent power module) replacement with new parts
- ▸Control power-supply and encoder-interface repair
- ▸Full recap as standard
- ▸Powered verification with a test motor where applicable
- ▸24-month warranty
Your program is safe
We preserve amplifier parameter sets where they are stored in the unit, and note anything your integrator should verify at reinstall.
Common part numbers we see
Part-number pages for this service
How Mitsubishi Servo Amplifier units actually fail
Most units we receive fail in one of a handful of well-understood ways. Here is what each fault looks like from the machine, what is happening electronically, and what we do about it at the bench.
Power module failure
- What you see
- Overcurrent alarms, or a drive that trips immediately when enabled.
- Why it happens
- The power stage fails short, typically as a consequence of a shorted motor winding or a damaged motor cable rather than on its own. The downstream fault must be found or the repaired drive will fail again.
- What we do
- Power devices are tested cold and replaced, gate drive circuitry verified, and the drive proven under load.
Bus capacitor degradation
- What you see
- Undervoltage alarms, or faults appearing only under acceleration.
- Why it happens
- Capacitance loss and rising ESR after years in service leave the bus unable to support acceleration current.
- What we do
- Bus capacitors are assessed and replaced and behaviour verified under a real load.
Overload and thermal alarms
- What you see
- Overload or overheat alarms, often after a period of running.
- Why it happens
- These can be a genuine drive fault, a cooling failure, or the drive correctly reporting a mechanical problem on the machine — a binding axis or failing bearing that is making the motor work harder.
- What we do
- We establish which of the three it is. If the drive is electrically sound and the machine is the problem, the evaluation says so.
Encoder interface faults
- What you see
- Encoder alarms, position loss, or an axis that will not hold position.
- Why it happens
- Damage to the feedback interface, frequently originating in an encoder cable fault at the machine end.
- What we do
- Feedback circuitry is repaired and position stability verified on a running load.
What happens on the bench
The same sequence on every 6-stage repair, 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.
Check these before you ship
Some of these will tell you the unit is fine and the fault is elsewhere. We would rather you find that out now than pay to ship a good unit.
- □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.
Repair or replace?
Servo and spindle drives are where repair economics are most favourable: the hardware is expensive, frequently obsolete, and often tied to a specific machine and parameter set. New replacements for older platforms are commonly quoted at multi-week lead times when they are available at all, and a like-for-like replacement still has to be parameterised and commissioned against the machine. Because a drive failure usually stops the machine outright, the number that matters is rarely the invoice — it is how many production days pass before the axis turns again.
What to ship
- ▸The amplifier only
- ▸The alarm code and machine make/model
Full packing guidance: mail-in instructions.
Ship your unit to
USPS
Control Board Lab
PO Box 120241
Arlington, TX 76012
UPS / FedEx
Control Board Lab
1009 Oakwood Ln # 120241
Arlington, TX 76012
Write your RMA number on the outside of the box and include it on a note inside. Units over 50 lb (large VFDs, spindle drives, industrial PCs in enclosures) ship by freight — contact us before ordering and we will arrange dock-to-dock shipping.
Frequently asked questions
MR-J2S is obsolete — should I repair or migrate to MR-J4?
Migration means new motors or adapter engineering, parameter work, and downtime. While a machine otherwise runs well, repairing the failed amp (typically $450–$950) is dramatically cheaper. We'll tell you honestly at evaluation if your unit is at the end of its economic life.
What does alarm AL.32 usually mean?
AL.32 is an overcurrent fault — most often a failed IPM power module in the amplifier, sometimes triggered by a shorted motor or cable. Our bench evaluation isolates which. The IPM replacement is the bread-and-butter MR-J2S repair.
Start with a free evaluation
Ship it in, get a firm quote, approve before any work — pay nothing if it can't be repaired.
The Fixed-or-Free Guarantee: if we can't repair it, you don't pay for the repair.
Call (817) 799-7332 · 📱 Text us a photo of your unit · Email repairs@controlboardlab.com