Nice find!
We still have one of these at work. No one ever uses it nowadays, but I used it quite a lot until about ten years ago.
I tried to power it up the other day and got the same high pitched squeal. Perhaps the "Oops I'm faulty....oh no I'm not" applies to this one as well
. Maybe I'll try it again next week.
The operation is indeed a bit strange when compared to more conventional layouts, but you get used to it quickly.
XY is called "X-deflect" on these scopes.
Your's looks to be a 1990 vintage, datecodes on the ICs are late 1989.
Now that your's is working, it's worth checking out the ripple voltages on the several (low voltage) rails. At 25 years old the electrolytics will have seen better days and that might show as elevated ripple.