Ok ... all tests now pass, both analog and high voltage. I still need to deal with the missing buttons on the front and a bit of tidy up (and a few more caps to do), but I think it's almost there as far as basic functionality goes!
Is the output voltage stable?
I've only just started to look at the output and there are lots of caveats to this ... the room is a bit chilly and I can feel cold draughts (although can't find a source) and I'm stringing two connected sets of cheap Chinese test leads across the room, neither the meter (DMM7510) or the 5440B are properly warmed up (probably about 90 mins at this point) ... ignore the absolute numbers, the 5440B isn't calibrated and the DMM7510 isn't self-cal'd ... so there is a huge set of error sources in this, however....
From the attached graphs you can see the output, this is from about 1 second after hitting OPER ... each time I run it the ultimate output seems very consistent and settles at 10.000417 (averaging over different time periods, using 5NPLC and no filter) although has been slightly rising in more recent attempts to 10.000419, I suspect this may be to do with things still warming up.
(Later note -- it's now at 10.000425 and has been consistently increasing, does look like a warm-up process)
The first graph (102055) is from a run where it wasn't at standby for very long, probably no more than 3 minutes ... it looks absolutely fine to me, the specs say it can take 10.5 seconds to settle to within 0.5ppm from STBY to OPER, and it's probably within 0.2ppm at that point.
The second graph (103148) is after a much longer STBY period, probably 10 minutes or so, and you can see a lower dip (from stable state), although still only about 0.6ppm, but it does then take a bit longer to stabilise which may well be to do with relay heating/equalising.
Either way I'm not sure I'm seeing a particular problem -- although I will look again once I've found less error-prone ways to measure this. To be honest I'm absolutely stunned how good this seems to be ... this thing has clearly been in a room with a fire, filled with smoke, filled with water, left to soak for a while, had all the really expensive relays replaced with different configuration low cost Chinese ones, and been messed with by a fairly incompetent idiot that only half knows what he's doing ... it's a miracle it's working at all!