The Bluetooth interface is driven by the MBB, but only when the contactor is closed (mainly driving, but also in charging mode).
The MBB always has some kind of power, so the OBD-II interface is the most assured way to get in there, but even then it may not respond unless it decides it's keyed on.
Well, I will give another try to check pin 1 voltage in the DC DC converter. I have tried connecting the multimeter's negative in the bike's frame and the positive in pin 1 and so far only a small measure (something like 0.1 volts). I will try connecting the negative to the B- input as Brian said. Or do I have to connect the negative terminal in another specific way in order to check pin 1?
I think the input in pin 1 has to be 12 volts when off and high (the voltage from the battery) when on. If there is no voltage at all, the problem could be the MBB, right? Could a failure in the MBB be the responsible for not having power at all?
I also checked the continuity of high voltage fuse 1 (low power b+) and it's fine but I just can't find the other high voltage fuses. I would be very interested in checking the MBB fuse but it isn't where the manual says! Does anyone have an idea of where it is?
I forgot to answer your question above. The MBB is responsible for signaling to the DC-DC converter to turn on, so it could be the cause, yes. However, it has been noted that a bent pin on the relevant line between the MBB and the DC-DC converter can have the same effect, so that's something to check just in case. Use Burton's S/DS schematic to be sure, if you need to look into that, but basically any bent pin would be suspect.
FYI, the one virtue of troubleshooting the DC-DC converter is that it is a generic component that can be bought off the shelf from EV vendors and swapped.
I wish I knew where your fuses were. Because your battery is upgraded, it may just be best to hand it to your dealer at this point.