JR East has announced the results of an investigation into a vehicle failure that occurred on the Yamagata Shinkansen “E8 series” train on June 17 (Tue), 2025, and has revealed future countermeasures and operation plans.
“Difference in current + temperature” was the trigger
On this day, train car failures occurred on four E8 series trains, including a deadhead train running between Utsunomiya Station and Nasu-Shiobara Station on the Tohoku Shinkansen, and damage to semiconductor elements was confirmed in a total of six auxiliary power units. In addition, on June 30 (Mon), a failure was found in one auxiliary power unit in another E8 series train that was parked at a train depot in Tokyo. The auxiliary power units that supply power to each device on the train are composed of semiconductor elements that convert power and a circuit board that controls it, and investigations have been continuing with a focus on this combination.
As a result, it was found that semiconductor elements manufactured after a certain period of time flow with a larger control current than conventional auxiliary power units. The surrounding temperature rises when a current larger than expected flows through the board, and this, combined with the temperature rise due to the heat, causes the protective element to operate incorrectly, cutting off the control current. The investigation concluded that excessive current flowed through semiconductor elements that could no longer be controlled normally, damaging the elements and causing the power supply to the main converter to stop, resulting in the train being unable to run.
Trip to Yamagata with a 5,000 yen discount coupon
This phenomenon does not occur with the combination of semiconductor elements and control boards installed in the E8 series before the 6th train manufactured by June 2024, or the Akita Shinkansen E6 series. As a countermeasure for the E8 series auxiliary power supply unit, the settings of the protection elements in the control circuit will be reviewed to prevent malfunctions due to differences in the current controlling the semiconductor elements and increases in ambient temperature. Vehicles for which countermeasures have been taken will be gradually returned to commercial operation after confirming their soundness.
Currently, the solo operation of the E8 series, which is currently suspended, will be gradually resumed from August 1 (Fri), and regular Yamagata Shinkansen trains will resume operation according to the normal timetable (some trains will be suspended only on August 1 (Fri)). Special trains will operate with reduced service from August 1 (Fri) to 8 (Fri), and the operation schedule for special trains from the 9 (Sat) onwards will be announced around July 28 (Mon). In addition, JR East will distribute 5,000 yen discount coupons that can be used for travel and accommodation in Yamagata Prefecture through JR East View Tourism & Sales, in an effort to attract tourism to Yamagata, which has been hit hard by service suspensions and reductions.
