That would be well beyond my knowledge and skill level I'm afraid. I started getting edgy when you mentioned a multimeter tbh. I guess you could open her up and check for any domed capacitors or obviously loose wires?
I did try shaking and hitting one of the cats, but the only "scratching" that happened was on my hand.
I managed to find a service manual with all the wiring schematics etc., but I'm pretty much (completely) out of my depth now. From it I gathered that there are three fuses, which I've checked and they're fine.
A couple of years ago I gave a perfectly working and reasonably modern JVC midi-hifi & speakers to charity during a house move. I regret doing so now.