My first suggestion is to get a 466 SERVICE manual,with the parts
lists,schematics,and VERY important;the CIRCUIT DESCRIPTIONS,which are very
detailed,and tell how each section of your scope work.

Try Ebay or www.big-list.com,TEK no longer supports this model.

In connecting to the AC mains,it's very likely that you burned up some
ground runs on circuit boards.

IIRC,TEK has some literature on why one should not make un-isolated
measurements with grounded scopes. www.tek.com.
--
Jim Yanik,NRA member
jyanik-at-kua.net