Wow, thanks a lot everyone of you for your help, much appreciated !
Shakalnokturn I sure vivdly remembered that you had a soft spot for these old Philips CD players, hence was hoping you would offer your help, thanks for doing so then !
So, to sum it up :
1) I was wrong then, no simple "CD presence optical switch", so no easy fix, bummer !
2) It can be a million different things I have mostly no clue or experience with, great !
As far as smoke/dirt on the lens : non smoking dad, and clean house...
As far as mechanical damage... the player has spent the last 30 years in the same comfy living room, never had "accidents", a peaceful life.
I noted that you don't all agree on one point : is the disc supposed to spin before, or after focusing is attempted ? I guess that means it depends on the particular drive/product...
As far as putting the disc the wrong way around.... OOPS, yes I did !
Indeed I put it label up, but indeed it's supposed to be label down, the head being atop of the disk. With the disc the correct way around, the CD player behaves 100% the same, nothing has changed.
Lens cleanliness ? It facing down, I can't even see it !
Disc clamping : can't see much of what's happening in there... once the player has drawn a tray from the cassette, the tray hides the bottom of the mechanism of course, so I can't see if anything underneath the tray is pushing upward to clamp the disc to the motor...
Laser working ? Here again, with the head facing downward, I can't see squat
How easy is the laser spot to distinguish ? Is it a large blurry blob that reflect off of the surface of the disc, and it is absolutely impossible no to see it ? Or is it a tiny 0.1mm spot ? I can't see anything (anything obvious I mean) reflecting on the surface of the disc. I also had a look when it's trying to read an empty tray : the interior is all all black plastic parts, so I turned all the lights of in the room to make it dark, and stuck my nose in there, thinking I would be able to distinguish a tiny laser spot easily on a black plastic part.... but I didn't see anything.
OK. Before I can do any troubleshooting I need to print all the schematics and block diagrams in A3 format at work so they are about readable. Will do that tomorrow. Until then I can only do thought experiments !
One question : this 2 second delay we witness, after the head has finished moving, and before it switches to the next disc... what does it correspond to ? What is the drive (trying to) doing during that time ? At first I thought it might correspond to the time during which the disc is supposed to spin, and during which teh drive is trying to read the disc. It it fails after 2 seconds of trying, then it gives up. However if that were the case then why would it do it even for trays where there is no disc, and therefore where we are sure it can't possibly focus.. if it can't focus why would it wait 2 seconds trying to spin the disc (or whatever), instead of just skipping immediately to the next disc ? Seems odd / inefficient to me...
That would make sens however if the focusing is attempted AFTER the disc is spinning... in which case during these 2 seconds, maybe it is trying to spin the disc but it just doesn't work. Hence investigating the spindle motor might still be useful....
So, questions and more questions !
Tomorrow once I get the schematics printed, I could start with :
1) Check all numerous power supply rails, first things first eh ! You never know... mayube the laser is indeed not working since I can't see anything, and maybe it's powered by a dedicated power rail, hence only the laser would stop working but it would not keep the rest of the circuitry from working.
2) Check the circuitry that drives the laser diode. According to the schematic it's quite simple. The decoder IC drives the LED via a humble NPN transistor (a BC338) fed by +10Volts. It also involves a 33uF electrolytic cap.... hum...
Could also test the laser diode itself with a basic diode test...
That 10V rail is not even listed as coming out of the 8 rails that the power supply board produces... so that's one more rail ! Will have to figure out how and where it is generated...
3) Check the turntable motor drive circuitry... it's made of a couple op-amps, from an NJM 4560 chip, whatever that is... then the final drive is a bi-polar push-pull stage, powered at the top by....oh, guess what... that same 10V rail that powers the Laser LED !
And... I see that the focus motor is also powered by that rail ! Ahhhh.... could it be just a faulty rail then ! That would be great !
... oh no, spoke too soon ! On another schematic page I see that the motors that handle the cassette and trays, also use that rail... and those motors work just fine. Oh well...
Still worth checking all rails of course, and local power supplies. You can't rule out local problems... just because the 10V rail works doesn't mean it gets to each and every place as it should... doggy flat flex, doggy local electrolytic cap, what have you....
I will try to attach the schematic but not easy. Even single sheets are too large to satisfy the requirements of the forum. If I compress a page enough to get below 500KB, then it's a bit hard to read :-/
I think best compromise would be to crop the schematic to retain the most relevant bit. This way picture will be smaller so I would be able to retain a high resolution / legibility without exceeding the 500KB file size limit..... just a bit time consuming that's all !