Is that correct? Voyager 2 launched before Voyager 1 (August 20 versus September 5, 1977. The numbering was chosen because Voyager 2 overtook Voyager 1), so it might have been switched on earlier, too.

Also (https://history.nasa.gov/computers/Ch6-2.html):

”Although both CCSs are always powered, rarely are both Flight Data Systems running, and both attitude control computers are never turned on at the same time.”

Can these systems be powered, but not running? https://www.allaboutcircuits.com/news/voyager-mission-annive... leaves that option open:

”The CCS typically remained on at all times, but the FDS would usually only operate one at a time, and the AACS would only ever operate one at a time. The idea was that regular dormancy of computer systems not actively in use would help maintain the lifespan of the systems.”