Take the back off then dig in......

[electra225]

The first thing I do when I get my new find home is to unload it outside, then remove the back. This is really more of a "honey-do" thing as much as anything. My wife has no patience for my hauling "some junk" into the house inhabited by a "critter". Having "her dress up" , removing the back, lets me get a good visual of what I have at the same time. I use the shop vac and an old paint brush to gingerly remove as much dust and dirt as I can. Also make written notes of any disconnected wires, cut or broken wires, missing or damaged tubes and components, that sort of thing. It's also a good idea to make notes of any model numbers you may find. You'll need those in order to obtain service literature for the instrument you are working with. If you see any mouse droppings or signs of mouse urine, typically spots or rust on the chassis ( and you can smell it) then it might be a good idea to remove any chassis or components sitting on the floor of the cabinet and check for nests or other debris there. You don't need to haul live spiders or mice into your dwelling or shop areas.