How to Fix Yaskawa G7 Drive Error PGO (PG Disconnection Detected)

Getting the PGO error on your Yaskawa G7 VFD? Learn how to troubleshoot PG disconnection, check encoder wiring, and verify power supply to your feedback device.

 

The Yaskawa G7 is a highly reliable drive often used in demanding applications requiring closed-loop speed control. When the drive displays the PGO (PG Disconnection Detected) error, it means the drive is trying to control the motor speed but has lost the "pulse" signal from the Pulse Generator (Encoder) that tells it exactly how fast the motor is turning.

Without this feedback loop, the G7 cannot accurately regulate speed and will stop the drive immediately to prevent an uncontrolled motor runaway. Here is your step-by-step guide to finding the break in the loop.

What Triggers the PGO Error?

The PGO error occurs when the drive detects that it is outputting a frequency to the motor, but it sees zero corresponding pulses coming back from the encoder. The most common causes are physical:

• Broken Wiring: A wire has snapped due to vibration or machine movement.
• Loose Terminations: The feedback cable has worked itself loose from the PG card terminal block.
• Wiring Errors: The phases (A, /A, B, /B) are swapped or landed on the wrong terminals.
• Power Supply Failure: The encoder itself is not receiving the 5V, 12V, or 24V it needs to generate a signal.

Step-by-Step Troubleshooting Guide

Safety Warning: Before checking wiring or opening the G7 cover, ensure the drive is disconnected from main power and wait for the DC bus capacitors to fully discharge.

1. Check Encoder Power Supply

The most overlooked cause of a PGO fault is a dead encoder. If the encoder isn't powered, it cannot send pulses.

• Use a multimeter to check the voltage at the encoder’s supply pins.
• Verify the voltage matches the encoder’s nameplate (e.g., 5VDC or 24VDC).
• If you have 0V at the encoder, check your PG card settings and wiring from the drive’s control terminal.

2. Inspect Encoder Cabling

Look for "weak links" in the feedback path:

• At the Motor: Check the junction box on the motor. Vibration often causes encoder wires to break right where they enter the connector.
• At the Drive: Ensure all terminals on the PG option card (e.g., PG-X2, PG-B2) are tightened securely.
• Check for Continuity: If possible, perform a continuity test on each wire (A, /A, B, /B, Power, Ground) from the motor side all the way back to the PG card terminals.

3. Verify Correct Wiring

Did this error happen after a motor swap or a repair? If so, verify your pinout:

• Compare your current wiring against the wiring diagram in the Yaskawa G7 technical manual for your specific PG card.
• Check for swapped channels (A and B). If the drive sees phase A but not phase B, it will often trigger a disconnection or signal loss alarm.

4. Check for Encoder Damage

If the power is correct and the wiring is sound, the encoder itself may be faulty.

• If you have an oscilloscope, look for a square wave signal on the A and B channels while rotating the motor shaft by hand.
• If you see no signal, the internal electronics of the encoder have likely failed and the unit needs replacement.

How to Reset the PGO Fault

Once you have repaired the broken wire or replaced the faulty encoder:

1. Clear the error by pressing the [RESET] key on the G7 operator keypad.
2. If the error persists immediately, verify that your PG parameter settings (such as number of pulses per revolution) match the physical encoder installed.
3. Cycle the power to the G7 if the fault remains locked in memory.

Maintenance Tip

In high-vibration applications, ensure your encoder cable is secured with strain relief. A PGO fault is almost always a mechanical wiring issue rather than a failure of the G7 drive itself. Taking the time to properly secure the cable today will prevent hours of downtime tomorrow.