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These are power-side alarms from the spindle drive: DC bus fuse, loss of an input phase, or a drive supply failure. They are not diagnosed from the panel and they are not reset to see what happens. The correct instruction here is to stop and call electrical maintenance.
For reference only: alarms change with the manufacturer, the control and the machine PLC. Check the full code in the official manual before doing anything. Legal notice.
Always, because it involves spindle power and electrical risk.
Do not reset until the power/drive/motor is diagnosed.
Choose the manual matching your control series, software version and machine builder. A support portal is a starting point; it does not establish applicability to every model.
The spindle drive is fed from the three-phase mains, rectifies that voltage and stores it in a DC bus from which the power stage draws whatever the motor needs at each instant. That path has several protections. One is the bus fuse, which opens when current flows that should not, typically from a short circuit in the power stage, a motor with degraded insulation leaking to earth, or a damaged motor cable. Another is input phase monitoring: if one of the three is missing, the rectifier cannot hold the bus up, the voltage oscillates and components suffer, so the drive cuts out before destroying itself. What has to be understood is the asymmetry of the risk. These alarms are not telling you the process is working hard, the way an overload does: they are telling you there is a real electrical problem upstream or inside the drive. Repeatedly resetting a condition like that is the most effective way of turning a blown fuse and one damaged component into a destroyed amplifier, and in the worst case of causing an electrical incident. That is why the correct procedure is not to retry: it is to lock the machine out and measure, which electrical maintenance does with the right equipment.
In order, from the fastest and cheapest check to the most expensive.
01Stop the machine and do not reset
Every reset attempt with a power fault present can make the damage worse. Leave the machine stopped, do not try to start the spindle, and lock its use out until maintenance has looked at it. This is not over-caution: it is what separates changing a fuse from changing an amplifier.
02Note the drive code and everything visible on screen
The spindle amplifier's alarm number, visible on the control's spindle diagnostic screen, separates a fuse from a phase loss and from a supply failure. Also note whether there are other simultaneous alarms and whether anything else in the shop tripped at the same time.
03Reconstruct the context without opening anything
What the machine was doing, whether there was an impact or a spindle jam, whether anyone noticed a smell, smoke or a sharp bang, whether there was a storm or a power cut, whether coolant has been getting where it should not. All of that steers you between motor, cable and drive.
04Check whether other equipment in the shop is affected
A phase loss on the incoming supply affects more than one machine. If other machines are also showing supply alarms, or something tripped in the main panel, the problem is the installation and not the spindle. This is checked from outside, without opening panels.
05Hand it to electrical maintenance with the machine locked out
Measuring phases, checking fuses, testing the insulation of the spindle motor and its cable, and inspecting the amplifier are jobs done with the machine de-energised, locked out and with proper test equipment. The operator does not open the cabinet, and a fuse is never replaced without first finding out why it opened.
06Do not go back into production until the cause is identified
A fuse changed without explaining why it blew will blow again, and the second time it usually takes something else with it. The machine goes back into production when there is a specific cause corrected and a satisfactory no-load test.
Suspect a short circuit in the motor, the cable or the power stage, triggered by the current peak. It is confirmed by insulation measurements, which maintenance carries out. Do not attempt to restart.
An installation problem: a lost phase, a protection tripped in the main panel, or a voltage dip. It is confirmed because several machines are affected. It is solved in the installation, not in the machine.
Degradation: spindle motor insulation on its way out, a cable damaged by chafing or coolant, or a loose connection that heats up. It is confirmed with periodic insulation measurements and thermography. Dealing with it early avoids the big failure.
Spindle motor insulation measurements inside predictive maintenance, especially on machines that use a lot of coolant. Tightening and thermography of power connections at scheduled services. Shop protection against voltage dips if the history justifies it. Sealing of glands and cable entries around the head. And a clear rule: with power alarms, the machine stops and you call; you do not reset it to see if it holds.
Fanuc can indicate DC link fuse, phase loss or power failure in the spindle drive. It is an alarm from the Spindle area, and in the catalog it is listed as “Spindle power fuse or phase”. On the machine you notice it like this: The spindle does not start, Spindle drive shows alarm, It may trip protective devices.
On the shop floor it almost always comes from one of these causes: Faulty spindle amplifier, Motor shorted to ground, Phase loss, Internal fuse blown. Rule out the most likely one on your machine first, before touching parameters or swapping anything.
Do not reset until the power/drive/motor is diagnosed. Resetting without fixing the cause first only hides the problem: SP9003/SP9004 trips again and, in the meantime, you keep working with the machine in bad shape.
With the machine stopped and in a safe state, start with these checks: Do not reset repeatedly, Note the spindle amplifier display, Check power supply only by qualified personnel. That alone will tell you whether it is the program or whether you need to raise a maintenance job.
With SP9003/SP9004 active, avoid this: Do not bypass safety devices, Do not manipulate energized electrical cabinet, Do not continue producing if the alarm reappears. Skipping any of these points is what turns a minor stop into an expensive breakdown.
Always, because it involves spindle power and electrical risk. If you are not sure how far it goes, stop the machine and report it: a repeat alarm always works out cheaper than a crash.
It is critical: there is a real risk of damage to the machine, the tool or a person. Leave the machine stopped, do not keep resetting it to see if it goes away, and call maintenance before producing again. Guidance reference. Always confirm the full text in the exact machine/control manual.
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