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Fanuc Servo Motor Testing

Fanuc Servo Motor Testing

Using a meter or megohm meter to diagnose a FANUC motor circuit should follow these basic guidelines. You can use the steps in this technique to check for shorts in cables, windings, or openings. Make careful to switch off all power sources to the equipment before beginning the test, and then separate the 3-phase motor connections from the drive end. Check the cable visually to make sure it is in good condition before starting the test.

Short to ground test

OHM meter usage:

Remove the machine's amplifiers and any power sources. Check the ground wire and the three wires at phases T1, T2, and T3 (all three phases). If the readings are 0 or show any continuity, there is an issue with the cable or the motor. The readings for this should be infinite. To do this, cut the cable, then examine each component independently. Make sure that neither of the leads, including the other leads, are touching anything. A standard grade meter set to at least 10 megaohms may be used to detect the majority of servo motor shorts.

Megohm meter usage:

Remove all power from the machine. Check the ground wire and the three wires at phases T1, T2, and T3 (all three phases). The recommended reading range is 600–2000 megohms. Most shorts will be 20 Megohms or less. When taking the reading, take care to avoid touching the leads or wires to anything as this might result in a misleading reading. Although this is not a universal rule, there should be around 1000 Ohms of resistance for every volt of incoming electricity. If it ranges from 230 to 600 meg, the cable could be degrading.

Open or short windings test

OHM meter usage:

Remove the machine's power supply completely. Test T1 to T2, T2 to T3, and T1 to T3 with the meter set to ohms. The typical value should be 0.8 ohms, but the range should be between 0.3 and 2.0 ohms. There is a short between the two phases if it is zero. The value will be infinite or significantly higher than 2,000 ohms if it is an open.

Take notes on plug and cable:

The cable connecting to the motor frequently develops coolant stains. Dry it out and retest; if the problem persists, replace the inserts since they will develop burn marks and may short out. Check the brushes if the motor is a DC one. Around the motor, there ought to be 3–4 circular caps to be removed. A spring and a square block (brush) are underneath these. As they might need to be changed, check to see how much is remaining.

If you need assistance in finding the drive, motor, or servo system you require, just let us know. We have access to a worldwide supply chain network and can locate exactly what you need. We also offer a wide range of other parts and components for a variety of machines and equipment, including:

  • Spindle Drives
  • Spindle Drive Motors
  • Monitors
  • Controls
  • Circuit Boards
  • Power Supplies
  • Rotary Tables
  • Other Motors

Our qualified customer service representatives can help assist you in locating parts for your machines and equipment, provide you with a quote, and help you set up maintenance, repair, or installation services from one of our qualified technicians. To further demonstrate that you are aware of what to look for, contact us at (956) 246-7411 or send an email to if you need any further assistance


Used, repaired, and rebuilt parts can be found in our inventory. We also have parts that were taken from functioning machines. To ensure that the part is delivered to our clients, each of them gets examined to ensure that it is in good working condition. We are able to provide a 10% price match guarantee program with written estimate thanks to our excellent global suppliers. With customer support available 24/7 and a readiness to help you with any inquiries you may have regarding any parts you've bought from us, CNC Tools LLC is constantly prepared to provide the most outstanding service to its clients. With more than 15 years of experience dealing with CNC machines, we are familiar with how our clients feel when their machines are down since this results in significant losses. As a result, we make every effort to offer a rapid and reliable service.

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