Yaskawa GA800 E78 Fault — What It Means
The E78 code is not confirmed in the Yaskawa GA800 manufacturer documentation available. Unlike verified GA800 faults such as oH3 (Motor Overheat from PTC sensor issues), E78 does not appear in the official fault tables. Always verify the exact alarm or fault code displayed on the drive keypad and cross-reference it with your GA800 manual or contact Yaskawa technical support before proceeding with any repair.
Because the meaning is unverified, the safest approach is to record the full code, note whether it appears as a fault or alarm, and gather your drive model number, serial number, and application details. If the code is temperature-related like oH3, wiring errors or defective thermistor connections are the most common culprits. Do not replace drive components until the code is properly identified.
Before You Replace Anything
Technicians sometimes replace the control board or power section before verifying the fault code and inspecting external wiring. Always confirm the code meaning and check motor sensor wiring, terminal connections, and parameter settings first.
Common Causes
- Unverified fault code E78 does not appear in available GA800 manuals, so the exact cause cannot be determined without consulting Yaskawa support or your drive’s specific documentation.
- Motor thermal sensor wiring fault If the code is temperature-related like the verified oH3 fault, defective thermistor or PTC wiring or wiring errors are common causes.
- Loose or corroded terminal connections Poor contact at motor terminals or drive input/output blocks can trigger fault codes and must be inspected first.
- Parameter configuration error Incorrect drive parameter settings for motor type, thermal protection, or input/output functions can cause unexpected faults.
- Control board or internal component failure Internal drive electronics may fail, but this should only be suspected after external wiring and parameters are confirmed correct.
- Incorrect fault code reading The displayed code may be misread or may be part of a multi-digit sequence that changes the meaning.
Quick Diagnosis
Answer these to narrow it down fast.
Does your drive keypad show E78 or a different code when you check the fault history menu?
No: Record the actual code displayed and look it up in your GA800 manual or contact Yaskawa before troubleshooting.
Is there a motor thermal sensor (PTC or thermistor) connected to the drive's auxiliary input terminals?
No: Focus on main power wiring, parameter settings, and contact Yaskawa to identify what circuit E78 references.
Does the fault clear and stay cleared after you power-cycle the drive and reset the alarm?
No: The fault is persistent and points to a hardware issue, wiring problem, or parameter error that requires further diagnosis.
Step-by-Step Fix
- Record the exact fault code displayed on the GA800 keypad, noting whether it shows as a fault, alarm, or warning, and check the fault history menu for additional detail.
- Consult your GA800 manual or contact Yaskawa technical support with your drive model number, serial number, and the exact fault code to confirm its meaning before proceeding.
- Inspect all external wiring connected to the drive, especially motor leads, control terminals, and any temperature sensor (PTC or thermistor) wiring for loose connections, damage, or corrosion.
- Verify motor thermal sensor circuit if the code is temperature-related by disconnecting the sensor leads, measuring continuity and resistance, and checking that values match the sensor specification.
- Review drive parameter settings in the programming menu to confirm motor type, thermal protection mode, and input/output configuration match your application and motor nameplate data.
- Clear the fault using the drive keypad reset function, power-cycle the drive, and observe whether the fault returns immediately or under specific load or speed conditions.
- Replace the identified component only after the fault code meaning is confirmed and external wiring and parameters are verified correct. If the fault persists after these checks, contact Yaskawa or a qualified drive technician for internal diagnostics.
Parts Often Needed
| Part | Notes |
|---|---|
| Motor PTC thermistor or temperature sensor | Amazon | Only if the fault is confirmed to be temperature-related and the sensor tests faulty or open-circuit. |
| GA800 control board | Amazon | Order by exact GA800 model number. Only replace after confirming internal board fault with Yaskawa support. |
When to Call a Pro
Call a qualified VFD technician or Yaskawa authorized service center if the fault code cannot be identified in your manual, if the fault persists after you have verified all external wiring and parameter settings, or if internal drive diagnostics are required. High-voltage work inside the drive enclosure and internal component replacement require proper lockout/tagout procedures, discharge of capacitors, and knowledge of drive electronics. Always provide the technician with your drive model and serial number, the exact fault code, fault history, and details of your motor and application so diagnosis can proceed efficiently.
Rough cost: A pro service call runs about $200-500 depending on diagnosis time and component replacement.