The lens fell out on this one. Every time I've gotten one that didn't read discs, it has either been a missing lens or a dirty lens. I have also gotten some where the motor made a bit of noise.
I just swapped in the whole left side (changer/laser/motor) from my PD-M510, since those parts were all identical. Doing all three made it really quick and easy, since the wires were all bundled together.
That is right. According to the Russian-maintained list of CD transports and DACs, the Pioneer changers in the early productions were of PYW1009/PWY1010. They read discs upside down (i.e. the printed side facing down on the cd tray/changer magazine). One of my friends told me that the missing lenses were because of brittle glue coming of age. He suggested using the lens from a Sony KSS-213 (A/B/C/D etc), and glue it back.
Later, I bought a Nakamichi CDC-3A six-disc changer with the same PYW1009 pick-up assembly, and the CD pick-up lens was absent. The seller of this CDP on the ePay site said it was non-working so I got it cheap. I bought 4 new KSS-213A lens and pick-up head for a song and used the lens from it to repair the Nak. Surprisingly, it worked after a little tweaking on the trim pots on the laser servo board. It sounds surprisingly good as it runs a TDA-1541A DAC of Philips, and the 4X upsampling from SOny CX1088.