I recently acquired a PCE Duo with CD reading error; I've already cleaned the board thoroughly and changed all caps, also made sure (to my really limited knowledge) that they all work well, no lifted pads or broken traces, but cd doesn't even want to spin.
I've read that the first step before adjusting pots is marking the "initial" point to be able to go back to safe settings, but the thing is that the former owner of the console told me that he "adjusted" them already.
A forum member kindly told me that TheSteve and Turbokon made a couple videos showing how to adjust them using an oscilloscope, but I haven't been able to find them, and the thing is that I don't have the knowledge to start fiddling with an oscilloscope without a proper tutorial or guidance...
What should I do?
Thanks a lot for your help. 
OK, I slapped some screencaps together, and the comment section of Steve's video has even more information to tune those 3 CD potentiometers like a pro, although it's "rough" so I'll try to make sense of what you must do.
** Proper CD waveform when tuning a CD laser/player **
https://www.facebook.com/steven.hanely/videos/10201717056086907/https://s5.postimg.cc/j65ephh2f/3_Pot_PCECDOscilloscope-01.pnghttps://s5.postimg.cc/i3v86y5yv/3_Pot_PCECDOscilloscope-02.pnghttps://s5.postimg.cc/anvyl6d4n/3_Pot_PCECDOscilloscope-03.pnghttps://s5.postimg.cc/3xfhbqxon/3_Pot_PCECDOscilloscope-04.png* You hook the oscilloscope to P5 pins 1 and 2 (1 is ground, 2 is RF signal).
* Pots VR101, VR102, VR103, VR104 each effect the signal differently
* Once you play with it for a min, you should get a feel for it.
* The signal is comprised of a sign wave with a fixed slope and varied amplitude.
* So when the pulse is taller the frequency is lower, the peak/frequency variances are in fixed steps causing a grid effect.
* Your adjustment goal is max amplitude with minimal line jitter.
* VR105 is your sync hold pot.
Anyway, best I can do at this time, it's a real tough job to translate "steve-speak" for the common man (
But I try on rare occasion like this YPbPr Component Guide we worked on together).
So, in a nutshell, you must get the CD waveform to look like [this] what it does towards the end of his video while adjusting the pots. Since you say a new laser was installed and the installer adjusted those 3 pots away from factory defaults, it definitely needs to be done right, and this may help you if you solve the spinning problem first.
Personally, I think using a slow-burned CD-R of a game may/might be a smart strategy, you get it fine-tuned with a CD-R and they'll all work which should -- in theory -- guarantee that the laser works with original factory-pressed silvers. Although you may need to test that in practice.
On the other hand, if you only have originals, don't play burned CD-Rs for fan translations or downloads, then maybe don't bother on such an idea - stick with an original factory-pressed CD for tuning.
Good luck!
