gianfri : Sorry I wasn't clear.
Booting on bench (5V PC PSU) :
Farfalla : LED goes on and stays on
PC82 : LED stays off (I have activity on data and address bus, so there's something going on, no address bus/data bus lines stuck, chip select looks right, reset line high then low)
Leon : Starts with blinking, triggering RAM test goes OK, goes into switch test - all switches off, setting DIP switch on shows switch light (so this is correct)
Booting in machine with driver card and sound card connected, switch connectors not connected :
Farfalla : LED on PCB stays on, displays show all zeros, LED on soundcard goes off (test button on soundcard works) - no attract lights blinking, though, unsure what's normal here
PC82 : LED on PCB stays off, displays show garbage, LED on soundcard stays on
Leon : LED on PCB blinks, controlled lights blink, LED on soundcard blinks
I tried PC82 booting with only displays, without displays, on bench ... no go.
I tried both 7-digit and 8-digit roms (machine is 8 digit).
I'm going to try to make 2764-ROMs out of the 2532 images and see if that works ...