Record diagnostic number 356 before turning off the power
When checking Fanuc alarm 364, diagnostic number 356 is a very useful clue. According to Fanuc maintenance information, this value should normally be 0. If noise or another factor affects the position data from the built-in pulse coder, the diagnostic value may start going up.
There is one detail that people easily miss: diagnostic number 356 resets to zero after the CNC power is turned off.
If you see the alarm and immediately shut down the machine, then remember to check the diagnostic value after restarting it, the abnormal reading is already gone. All you can do then is guess.
The right way is to avoid restarting or turning off the power as soon as the alarm appears. First record the current value of diagnostic number 356 and save the full alarm message. That gives you some actual on-site data to compare when you later check for interference or inspect the pulse coder.
Of course, one reading alone doesn't prove that the pulse coder is faulty. You still need to look at the alarm condition, machine model, and what the machine was doing at the time. But the value can at least help you judge whether something disturbed the position data.
Electrical noise is invisible, but it can cause a lot of trouble
If alarm 364 only appears now and then, or the machine's electrical wiring was recently changed, or some high-power equipment was newly installed nearby, pay close attention to electrical noise.
In a servo system, the motor power cable and pulse coder feedback cable each have their own job. If the cable routing, shielding, or grounding no longer matches the machine's original design, or someone moved the cable bundle during a repair, the feedback signal may pick up interference.
At this point, find the machine's electrical drawings if possible. Follow Fanuc's requirements and check the pulse coder feedback cable, connectors, shielding, and grounding.
This matters even more on a machine whose electrical cabinet was recently repaired. The original cable route and shielding connections should be restored properly. Don't add a ground wire, change the shielding method, or retie the cable bundle just because it seems convenient.
Every machine has its own electrical design. An experienced technician should deal with these points according to the machine's actual configuration.
If the noise source has been found and dealt with, but alarm 364 still returns, don't keep restarting the machine. Continue checking the detector itself.
Coolant getting into the pulse coder is common on older machines
Machining centers and CNC machines work around coolant every day. The motor and nearby parts are exposed to it for years. If the detector or related connector isn't installed properly, coolant can work its way through a gap and enter the pulse coder. Once that happens, position detection may be affected.
A few repair histories should make you especially careful:
- Someone worked on the pulse coder connection.
- Coolant leakage was already found before the alarm appeared.
During inspection, look for signs of coolant around the pulse coder and its connectors. Also check whether the pulse coder and plugs are installed correctly.
The Fanuc maintenance manual also says that incorrect installation of a sensor or connector may allow coolant to enter the sensor. If the damage is serious, the pulse coder may need to be replaced.
If you suspect that coolant has already entered it, don't spray cleaner inside or take it apart using a method you're not sure about. Follow the correct maintenance requirements for that Fanuc motor and detector. If coolant has entered the unit and affected normal operation, the damaged part needs replacing.
If noise and coolant have been ruled out, check the built-in pulse coder
Suppose you've checked diagnostic number 356, dealt with possible electrical noise, and found no sign of coolant around the detector, but Fanuc alarm 364 still keeps coming back. The next step is to test the built-in pulse coder more closely.
First confirm the actual servo motor model, detector configuration, and the exact conditions under which the alarm appears.
Different Fanuc servo motors don't all have the same construction. On some motors, the pulse coder can be handled separately by following the correct maintenance procedure. On others, you need to consider the design of the complete motor assembly.
Before ordering a replacement, confirm the full servo motor model and pulse coder configuration. Don't assume a certain pulse coder will fit just because the machine shows alarm 364.
One more thing: don't replace the
servo amplifier just because alarm 364 has appeared. The main issue here is abnormal data from the built-in pulse coder. Only test the amplifier or other related hardware when the inspection results actually point in that direction.
Don't mix up alarm 364 and alarm 384
Fanuc also has alarm 384, which is another soft phase alarm. The difference is that alarm 364 is for the built-in detector, shown as INT, while alarm 384 is for an external detector, shown as EXT.
Before troubleshooting, confirm the full alarm message and the actual
encoder configuration used on the machine. Don't mix up these two fault types.
If you follow the alarm 384 troubleshooting path for alarm 364, or do it the other way around, you'll be looking in the wrong direction and wasting a lot of time.
Before replacing anything, confirm the motor and pulse coder models
If the final checks confirm a problem with the built-in pulse coder and it needs repair or replacement, don't place an order too quickly.
First collect the full servo motor model, pulse coder configuration, CNC model, and alarm axis number.
Different Fanuc motors may use different pulse coders. Their installation methods, absolute position settings, and related parameters may also be different. Don't take the experience from another machine that "looks about the same" and apply it directly to this one.
When replacing a pulse coder, you may need to deal with the absolute position, detector installation, and related parameters again. If this work isn't done correctly, it can bring up new alarms.
A word about safety
Inspection of the servo motor, pulse coder, and related circuits should be carried out by technicians with the right experience. They also need to follow the safety requirements from Fanuc and the machine builder.
Before unplugging connectors or checking circuits, make sure the equipment is in the required safe condition.
If the pulse coder needs replacing, first confirm the matching motor model and correct maintenance procedure. Absolute position setup, detector installation, and related parameters may vary between system configurations. Don't copy the procedure from another machine without checking.
In the end
Fanuc servo alarm 364, also called SOFT PHASE ALARM (INT), mainly concerns abnormal position data from the servo motor's built-in pulse coder.
The most important point is simple: don't treat alarm 364 as proof that the servo amplifier has failed. Find out what is really causing the bad position data, then decide which part needs repair or replacement. That saves money and helps get the machine back into stable operation sooner. If you really can't handle it, come find us at
SongWei CNC.
