From memory: remove all screws, unplug all ribbon kables, pull out the chopper led contacts, unplug the 3 coaxes (if present), lift out upper board, done.
I presume the coaxes are removed at the board end, and not by soldering (cf the delay line in Tek 465).
I assumed the two PCBs should be removed as one unit, then separated, worked on, then reunited, and the unit reinstalled in the case. In my 7075 there are two sets of contacts, the chopper LEDs (B5-B8) plus four (B1-B4) near the short edge. The latter are completely
between the two boards, which makes it bizarrely difficult to position them correctly when the bottom PCB is attached to the case and the top board is being lowered inside the case.
I know software engineers can be, um, intellectually challenged, but I've usually found mechanical engineers to be a little more, um, realistic.