You can fix downloading SP1b thenDo not turn on YD until you switched the IRS to NAV and you waited at least 2 or 3 seconds, then, the switch will work correctly.However, If you are having the problem, without reloading the entire flight, just switch off flt control switch B to reset the YD logic, then turn it back to on.

From pic above you have no electrical feed to the YD. You have Batt Aux & APU selected even though the UPU is off. You have engine bleeds on but need to select 'Gen 1 or Gen 2'. Once you correct this the YD will work.

No, it's not. Look at you AC panel, you have APU secleted. This needs to be set at Gen 1 (Engine 1 or Engine 2 Gen 2) to supply power during flight. APU is switched off in your pic.

Just turn gen 1 on & reselect YD off & ON & it will stay arm & stay on.

I do trust you but you picture shows Engine bleeds on which is correct but your power panel is on APU which is off. I used to fly the 200 series of this type & ac gen should be on gen meaning generators (engines) so that the aircraft systems like YD are powered by more than just the battery.

Please don't get personal.

Time to have a look at the Fcoms again !!Fred.

I hope that this rapid refresh will help who is not aware about the electrical systems.However, the FCOM vol 2 will give more detailed informations, better explained and with electrical scemes.