Blackmail,
I forgot about the LGTU.
By way of clarification I have no schematics with me...
The checklist for the Landing Gear Jammed in the Up Position directs one to cycle the speedbrake to relieve System A pressure after System A pumps are turned off....presumably because check-valves in the system mean that system pressure at the LG, even though the relevant pumps are turned off, is still high.
Somehow you need to relieve this and return it to the reservoir?
Similarly, even if you turn System B pumps off, will this be enough to relieve the pressure at the LG?
Maybe you still need to cycle the speedbrakes (because outboard flight spoilers are powered by system B) to relieve system B pressure whilst manually extending the gear?
Like you say, presumably I need to make sure the gear
is down and locked else when I power up No 1 again, the gear may retract?
Curiously....