MacBook Air A1466 'sudden death': MLB defect
1 - 2 hours
Apple MacBook Air suddenly decided to quit, no apparent reason.
Back-up of data, but not of all installed programs and their settings, including stuff like painstakingly tweaked 3D printer driver.
Downloading circuit diagrams and testing with DMM and scope did not really reveal cause, noticed some 2 or 3 caps connected to PPBUS_G3H becoming very hot though, suspected near-shorting or whatever.
Removal of these made no difference.
Apple Centre quotes high replacement cost and advises loss of SSD contents (data & programs)
Ordered replacement Main Logic Board ('mid-2012') from IFixit.
Arrived 2 days later (US to EU).
Installing board is fairly easy. And SSD turns out to be the 'treasure-chest' indeed: computer starts up with everything the way it was. Mission accomplished.
Too bad the root-cause of the original problem remains unclear.
Find an SSD SATA or USB converter and make back-up (image ?) of SSD contents.