From a 2013 thread about one of the other two Twiggy Macs:
@OldMacGuy - Sounds like a good first step will be to find someone (ideally) local with a Lisa 1, who should be able to read and back up your disk over a serial connection to a modern computer. I'd recommend pursuing a backup now before continuing to test your drive with that disk, so you don't lose any data or corrupt the disk during your testing!
As for the drive itself, there's been some good discussion about Twiggy servicing over at LisaList2 lately. Perhaps you'll find that useful at a starting point:
If the controller board on the drive is identical to the one used in a Lisa, I wonder if the whole drive could be hooked up to a Lisa 1 and "exercised" by BLU, which would give you an indication as to whether or not it's working properly. Obviously, you'd have to make *absolutely* sure everything was identical before attempting this...
I didn't try these tips, but I will keep them on file for future reference. I ended up doing a clean install of the operating system and removing AfterDark. As far as I can tell the problem has been solved. The user is no longer experiencing crashes and error messages. The only thing he currently complains about is the loss of his screensaver.
At the risk of stating the obvious, you don't have the rear power button in the always on position, do you? There is a button with a little slot in the ps at the rear of the machine that could be set to be always on, presumably for servers.
Button at the lower left (on a Q650, but this is the same thing ps-wise):