tcasblue,
According to my B744 notes, Hyd Sys 1 physically has nothing to do with the spoiler/speedbrake system whatsoever. Only Hyd Sys 2,3 and 4 power the spoilers. However, by design (thank you Mr Boeing) the PSEU must see a signal from both Hyd Sys 1 and 4 plus aircraft on ground and thrust levers at idle in order for the auto speed brakes to go to full deployment.
If the PSEU does not see a Hyd signal from Sys 1 and/or 4, or thrust levers not at idle, or landing gear tilted (body truck not down and locked) then the auto speed brake actuator will retract and the speed brake lever will remain in the Armed position until it is physically moved to the full UP position and all spoilers go up to 45 degrees.
What the nose gear has to do with anything I have no idea and no mention in my notes. Methinks the QRH has thrown up a curve ball without clear explanation.
Rgds McHale.