Just some notes, should someone find them useful... Or if I ever need to debug them again.
First, a Pioneer PD-M450. It cost me 8 eur and was supposed to be in working order. On some CD-R's it would have repetitive static and noise at about the disc spin rate. Grabbing the flex cable to the pickup with my fingers made it worse. The only thing that made it lessen was turning the laser power up (because it made the signal stronger, I guess). I actually left it "fixed" like this and used it for a while. I wasn't happy with it though, so recently I opened it up again, turned the laser pot back to where it was and started over. I noticed that the problem only appeared with the cover on. The PD-M450 is a rather slim unit, and you probably guessed that the printed flexible cable was rubbing against the "ceiling". I taped a piece of foam on the cable to keep it away from the metal casing, and the problem seems to have gone away. I'm hoping that the 10-20 hours of use with higher laser power didn't affect its lifespan too much.
The second unit was a PD-M701. Cost me 6 eur, broken. It had all kinds of weird problems: would start to play then abort, would not recognize discs, would ignore some commands but not others etc. Cleaning or adjustments made no difference. The repairfaq mentioned a problem with white printed flexible cables, and this player had one. Moving it around while playing confirmed that the cable was to blame. The "fix" involved folding the broken part of the cable into a bight and taping it together... This apparently forces the broken strip ends together and the tape keeps it from moving. I know it's just a temporary fix, but it's my own player so what the hey. Pioneer Finland hasn't yet told me what the cost for a new flex cable is. The player is very nice otherwise, with a quality feel to it that the PD-M450 doesn't have.
Rambling on, Ilkka