This one is hard work ... this evening's shenanigans...
Firstly I transplanted the backplane out of the good scope into the new chassis. This was one of those moments where you think "will this thing ever end up back together?" and wish you never started the job. Found a couple of wiring errors which I corrected. No functional difference just the wrong numbered points used compared to the schematic.
Then the top chassis was reassembled into the bottom half. If you were a scope it looked like a horror movie around my corner. This is the next moment of regret where you think seriously about just buying a damn Keysight unit and leaving all this stuff in the garden and hoping by the morning someone had magically made it go away. Either that or you NEVER go in the garden again. I call it "repair regret" (why did I buy this pile of s**t; what was I thinking?)
Back together and powered it up. HT is still wonky but I expect that. This is just the first stage of the rebuild. After arguing with it a couple of times until the HT decided to wake its shit up, vertical is working. There is no horizontal sweep yet as the plugin has been bodged by the previous owner and doesn't work unless the rails are way off which they aren't now! It does sweep with the cal plugin.
Now one really cool thing is the trace is crispier than a crispy thing from planet crisp. Shot in X-Y mode. Not bad for a 42 year old scope:
Motivation returned. Never give up!