Not so techy but quite nerdy... I found an old Denon DVD/CD Dolby Digital amp in a junk pile, listed as "disc unfunctioning". Which seemed like a challenge...

Top off...



Straight to the likely cause...



Gears removed...




Replace old belt...





For good measure, clean the insides with compressed air and reinitialise microprocessor by holding "Play" and "Stop" while powering on:



And test:



This is now in my living room, unobtrusively powering four B&W speakers and a subwoofer with fine tunes.

Not too bad for an outlay of ¥1000 (about £6.50)

TT