Yaskawa SGMG-13VSAAB: investigating a speed feedback fault

An alarm appearing as soon as a servo motor is connected may draw attention to its encoder. However, an alarm alone does not prove that the encoder is defective. Cables, connectors and the correct drive configuration also need to be checked. This workshop case concerns a Yaskawa SGMG-13VSAAB with a confirmed feedback fault and additional mechanical damage.

Motor and technical data

The SGMG-13VSAAB is a Yaskawa AC servo motor. The servo amplifier supplies the motor while the encoder reports rotor position. The drive also uses this feedback to determine speed. The complete model designation matters when matching a motor, encoder and amplifier.

Motor ratings are taken from the corresponding product listing. Always compare the actual nameplate and machine configuration before selecting a replacement.

Symptom: A.51 during inspection

The workshop recorded alarm A.51 immediately upon connection, described as “Feedback overspeed”. Inspection confirmed a defective encoder. A damaged power connector and bearing damage were also found. Winding and insulation checks did not reveal a fault.

Alarm definitions depend on the exact servo amplifier and its version. The motor designation SGMG-13VSAAB is not sufficient to establish a universal alarm list. Identify the amplifier and consult its matching Yaskawa manual before troubleshooting.

Fitted encoder: Yaskawa UTMAH-B15ASB

A Yaskawa UTMAH-B15ASB 15-bit absolute encoder was fitted during this repair. The installed replacement part confirms this designation. The encoder measures rotor position and supplies the feedback needed by the servo control system. A faulty feedback signal can prevent the drive from operating.

Repair information and enquiries are available directly in our shop: https://www.industrypart.com/products/yaskawa-utmah-b15asb-absolute-encoder-15bit-38219.html

Matching the model name does not replace a compatibility check. Please include motor and encoder nameplate photos and the exact servo amplifier model with your enquiry.

Narrowing down the cause

Record when the alarm occurs: during power-up, when the drive is enabled or only during motion. Inspect connectors, cables and visible damage. Work on connections must be performed with power isolated and after the manufacturer’s discharge requirements have been met. Do not apply insulation test voltage through connected encoder electronics.

The feedback system can then be examined using suitable test equipment. Swapping encoders or amplifiers without checking their configuration may introduce further problems. Follow the applicable adjustment and commissioning instructions after work on the feedback system.

Workshop example: overhaul and final inspection

The motor was dismantled, derusted, cleaned and dried. Both bearings, the shaft seal and the broken JL04V-2E20-15PE power connector were replaced. A replacement UTMAH-B15ASB encoder was fitted. The brake was checked and was not replaced. Assembly and adjustment were followed by functional testing. The repair record confirms completion as repaired and tested. The available records do not specify a test load or duration.

Prevention and enquiries

Damaged connectors, cable strain, moisture and unusual running noise should be investigated early. For an efficient enquiry, send the complete motor and amplifier designations, the exact alarm and a brief description of when it appears.

Motor, repair and enquiry: https://www.industrypart.com/products/yaskawa-sgmg-13vsaab-ac-servo-motor-17327.html

Sources and scope

This article is based on the documented workshop findings, repair and test records, and the industrypart motor and encoder product pages linked above. This individual case does not establish a universal diagnosis for every drive in the series.

Price, Lead Time and Further Information

Current repair pricing and service options are shown on the motor product page linked above. We confirm a binding quotation and completion date after inspecting the motor and checking parts availability. Please include the motor model, amplifier model, alarm message and nameplate photographs with your enquiry.

Components replaced

Workshop photographs

Video: repair and functional test