Fingers crossed. Although if I'm honest I'm dreading looking at the channel problems. There's just no signal on either 2 or 4. The plan is to compare the voltages on channel 1 and 2 when in the same state and see if there are any differences anywhere. There are large defined objects such as opamps which I can check voltages on. If not, it's old fashioned signal tracing with a generator plugged into the channel and work back from the front end to the ADC and see what happens. I've got the schematics for an earlier revision of the device so I can trace it roughly and go from there.
On a positive note, I didn't have any bas40's or any schottky diodes. I probably do somewhere but I couldn't find them. So I just jammed two 1n4148's across the burned hole where the bas40 was.
Bingo. Whole panel works now
Shitty but it works:
Fortunately with these, apart from a couple of usually reliable ICs, they're chock full of standard parts. All SMD but easy to work with as they're quite large parts. Smallest is 0805.