Have you noticed that when you play a disc with batteries, the optical out never red?
As far as I know, the PCDP will open its optical out only when it's powered by external power supply.
Check such conditions at...
The teeth of the gears on the laser should broken; it happens commonly on every D50.
I have all documents you need but its circuit is durable, so basically service manual doesnt work.
I cannt see your pics in your link but I know the DPC77.
It's necessary to replace all capacitors inside of the player, then inspect its circuit and laser.
You can try if you can.
If you need help from me, you can contact...
It needs circuit inspection and repair. D35 seldom has this problem.
The common problem with D35 is horizontal skipping and the main motor should be replaced.
If you need further service, contact me by email@example.com