Thanks for the additional information, blueraven, thesteve.
Firstly, I have already applied white lithium grease to the worm gear and the laser rails. Handy stuff - I've used it to prevent my original N64 controllers from wearing out, and despite being 19 years old, those controller sticks snap back like new.
Just about the only thing I could do to my Duo is replace the HOP-M3 laser. I might do that anyway, though I have a horror of re-dialing the pots in again, even if I think it would be a worthwhile experience.
I'm a recent convert to the Church of PCE (having gone the long way 'round, from Nintendo to Sega to Atari to Sony to SNK to NEC), but I'm more interested in the technological side of things, so it occurs to me to wonder about the three connectors (P5, P6, and P7) on the Duo.
Obviously, they are for testing and calibrating the CD functionality. The trimpots on the board indicate to me that something about the CD's circuit was, shall we say, 'flexible'. Otherwise, there would be no need to include trimpots for adjusting the laser. My personal theory is that the lasers themselves have (or had) some pretty wide tolerances, but I can't confirm that.
What I am almost completely certain about is that the P5, P6, and P7 connectors are used in bringing those tolerances into the tight range required for launch-day perfection. Ergo, there must be some actual required values generated by these connectors that can be brought into conformity with the specs needed for flawless playback of OEM games. Extrapolating from that, there must be a document related to the practical difference in playability between a pressed disc (of any time, not necessarily a game) and a burned one.
I know this is somewhat stream-of-consciousness here, but unless I am very much mistaken, there must be a document detailing these values. It would be fascinating to collect and collate all this information...hmm.
