Traditionally, the Hydra has used a +12V AC/DC module and a +5V buck converter on the logic board, and then +5 is fed back to the AC board to run the relay test.
It's only now just occurred to me that this is a little bit backwards.
The circuit needs a lot of +5v power, but only needs +12V for two purposes: to feed the charge pump to make -12 and for the pilot generator.
It probably makes more sense to put a 5v AC/DC supply on the AC board and a +5->+12 boost converter on the logic board for the +12v needs.
Not sure when (or if) I'm going to make this change, but I'm at least going to look into it to see how feasible it is.