I have an Aiwa NSX-MT960 bookshelf system: the biggest baddest (lol) system you could get from them in 1998. It's been well used but not abused, has stayed solid and still works great (except for typical things like tape deck capstans and a flaky volume pot) after all these years. Except recently, for reasons unknown, it will "lock up" and need to be unplugged to reset, after which it's fine for a few days until it "locks up" again.

Symptom is it's turned off (on standby) with nothing on the display but the clock. Come by sometime later and the display is completely blank except for a tiny flicker in the lower corner. Pressing buttons on the console or remote does nothing. Unplug the console, plug it back in and it resets to "demo" mode and all works well, normal and proper.... until it locks up again at some random point days later. Nobody is yet to see the lockup happen in the moment, and all other devices nearby on the same circuit are fine.

While I'm aware there are better options to replace it with... I'm sentimentally attached to this and would like to be green and fix what I've been otherwise happy with. Plus it's almost retro-gimmiky-cool now. I should be able to fix this (and the volume pot) but all the same, before I rip it apart I guess I'd like a hint where to start. Approaching it like a pinball board "locking up", could it be a flaky timing crystal? Aged-out caps? Something else? How best to troubleshoot such a random, intermittent problem?