The problem was a 12 k resistor on the plate that feeds the diode, it was simply missing.
Lucky you, you found it
Sometimes they just burn away, check out this 3D printer boards SMD fuse F2, it just evaporated:
It was a self healing polyprop SMD1206, 5V, 2A, cause was a short. The user said there was a bang and some magic smoke.
However, it did what it was supposed to do, protected the 5V µcontroller area. Easy to fix too.
Also i remember a Grundig Fine Arts amp: their power supply provided 24V behind a rectifier, and they had to break it down to 5V. They used a diode to reduce to 16V, then a 0.25W resistor to burn some more energy and as a fuse. You could tell that it was indeed supposed to be a fuse because it stood alone and far from the board and was one of those that don't actually burn, but just smoke harmlessly away. After that some voltage regulator burned away the rest and provided 5V.
The resistor was gone, just the legs left, flapping in the breeze. The user reported a pop, some magic smoke and then the amp stopped working.
The resistor was supposed to protect the 5V section, but over 30 years or so it burned away it's 0.25W and aged, and eventually failed during normal operation. Easy fix too, albeit with a regular resistor, because those special non-burning ones are hard to find these days.
Anyway, glad you fixed your CD player, would have been a shame really.
I'm looking for a CDX 810, 910 or 1010 in silver for my own collection, around the same time:
I hope for one as good as this one: