Wow, it really is all in the liquid flux! I reflowed all the SMD chips really nicely and quickly. I applied power, but, alas, nothing. How depressing. However, I starting poking around U1D for no good reason and shorted two of the pins and the light came on! (Yeah, I know it's very bad practise to short things when the power is on but I was feeling a little pissed). Anyway, this gave me new hope, so I gave U1D lots of TLC and 8 shiny new joints.
And it worked!
Onto the Gamma 2 now (with the flux pen at the ready, this time!!!)