The
Chicago Tribune reports:
Burnt circuit boards snag Japan Boeing 787 probe
Circuit boards that control and monitor the performance of the plane's lithium-ion battery unit were charred and may be of little use to the teams investigating why the battery effectively melted, forcing safety investigators to scramble for possible clues from other components in the plane's electronics...
Japanese safety officials plan to take the damaged circuit boards to the manufacturer, Fujisawa-based Kanto Aircraft Instrument, for a detailed inspection.
The PCB's are large and possess significant monitoring/management capability. As has been stated, the protections failed to prevent thermal runaway.
Let's hope the ANA units are testable and yield good information.
Best outcome may be discovering a bad batch of PCB's.