FANUC
FANUC Power Supply Module Repair (PSM / PSU — A06B-6077 / 6087 / 6110 / 6120) — Mail-In
Component-level repair for FANUC power supply modules feeding alpha/alpha i servo systems. Rectifier bridges, bus capacitors, and control supplies are the classic failures. Free evaluation, typical repairs $500–$1,200.
Coverage: PSM series — A06B-6077, A06B-6087, A06B-6110, A06B-6120 and related
✓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
- ✓PSM alarm LEDs / no ready signal
- ✓Whole servo system dead
- ✓Trips main breaker on power-up
- ✓Intermittent bus undervoltage faults
Honest limits
- ✕Incoming 3-phase supply problems at the machine (we'll tell you what to check)
What you get
- ▸Free bench evaluation and firm quote
- ▸Rectifier and precharge repair
- ▸DC bus capacitor bank replacement
- ▸Control power-supply repair
- ▸Fan replacement, full recap
- ▸24-month warranty
Common part numbers we see
Part-number pages for this service
How FANUC Power Supply (PSM) 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.
Pre-charge circuit failure
- What you see
- The module will not bring the bus up, or alarms immediately on power-up.
- Why it happens
- The soft-charge circuit that limits inrush while the bus capacitors charge — the resistor and its bypass contactor or relay — is a genuine wear item, and its failure stops the bus reaching working voltage.
- What we do
- The pre-charge path is tested and repaired, then correct bus charging is verified through a controlled power-up sequence.
DC bus capacitor degradation
- What you see
- Undervoltage alarms across multiple axes, or faults that appear under heavy machining load.
- Why it happens
- The supply module feeds every drive on the machine, so degraded bus capacitors produce faults that appear to come from several axes at once and are routinely misdiagnosed as multiple drive failures.
- What we do
- The capacitor bank is assessed and replaced and bus stability verified under load.
Input rectifier or power device failure
- What you see
- No bus voltage, blown input protection, or evident internal damage.
- Why it happens
- Failure of the input rectification or regeneration stage, sometimes triggered by a supply disturbance upstream.
- What we do
- The input stage is tested cold and repaired at board level, and full function verified under load.
Cooling failure
- What you see
- Overheat alarms on the supply module during sustained machining.
- Why it happens
- Fan failure or heatsink obstruction, aggravated by the continuous load a supply module carries for the whole machine.
- What we do
- Cooling is restored and thermal performance confirmed under sustained load.
Because the power supply module feeds every drive on the machine, its failures masquerade as multiple simultaneous axis faults. If several axes started alarming at once, the supply module is a more likely single cause than several drives failing on the same day.
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 PSM only
- ▸Alarm/LED state + 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
My whole FANUC servo rack is dead — amp or PSM?
When every axis is down at once, the shared PSM is the first suspect. Its LEDs (or lack of them) usually tell the story. Send the PSM first — it is the common single point of failure, and the evaluation is free.
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