After watching those videos, here's my summarization of what happend to AI171

• During the roll, somewhere inside main battery diode and/or main battery shorted caused left instrument bus to short to ground
• Remaining non essential 28V bus (including the power supply to fuel valve actuator and the remote data collection unit) continued to operate with 28 V supplied via the main battery charging circuit and the main battery discharge diode.
• Bus tie spread the issue to the right side instrument bus (jugding from staggered engine shutdown, right side shorted about 1 sec later than left)
• "Run" coil of the spear valve solenoid was de-energized from the left instrument bus, energy stored in the parallel capacitor caused the solenoid to misfire into the "Shutoff" position (this misfiring behaviour is specified in the solenoid's manufacturer).
• The LED of the photocoupler on the fuel control switch circuit was de-energized due to left instrument bus shorting.
• The fuel value actuator starts to close the fuel line, engine was shut down due to solenoid misfiring into "Shutoff" position. And due to de-energized photocoupler LED, the remote data collection unit sees signal from the fuel control switch to transition from "Run" to "Shutoff" (Which it technically shouldn't, because the photodiode of the "Shutoff" position is also de-energized, but the loss of power may be staggered due to induction? But this also explained the bad wording in the preliminary report)
• when 28V instrument busses short circuited, 235V-28V transformer rectifier protected and stop drawing power from 235V bus
• Due to continuous lose of power withdrawn from 235V busses from 4 generators, RAT was immediately commanded to deploy, the signal is able to pass through the bus power control unit which is still powered normally by the non essential 28V bus. (RAT was not deployed by engine shut down, because that requires a 15s delay, which would mean in this case the RAT would deploy after the fireball)
• APU charger input was shorted to ground from the right instrument bus, but the charger isolated the issue and allows APU computer to still have power supplied by APU battery which allowed APU auto start in the later part of the flight.

Left instrument bus controller can detect fault via battery charger, either imbalanced cells or short circuited battery, but will only cut the main battery solenoid if the fault signal is continuous for 15s and the airplane is not on battery power only in AIR mode.

So to reconstruct some critical times from the preliminary report:

• ENG 1 "fuel cut off switch transitioned from 'Shutoff' to 'Run'" means that the short circuit situation has been resolved, photodiodes and fuel valve solenoids are working correctly from that point.
• Left instrument bus short circuit resolution was from left bus controller disconnecting the now faulty battery
• Trace back 15s, the initial fault happens at around 2s after Vr
• From the time published in the report in which RAT starts to supply electricity and hydraulics, the critical short circuit event and RAT deployment happened at around the time where the gear up instruction is commanded.
• RAT just started to supply power to all busses for 1 sec before the faulty battery was cut by the bus controller, from now on there is no electric fault in all busses and this allows engine re-ignition.
• Right side instrument bus recovers after the left side, which is normal but caused ENG 2 to delay its re-ignition even further.

Si-denote:

• Boeing has signed a contract with Cyient DLM to produce new main battery diode module in 2024/07, suspect that Boeing knew the problematic module early on.