For repair I got a professional Denon DN-961FA on the workbench.
Symptoms: Could not read CD.
It’s a very well build and stable CD-player. Seen a lot in radio broadcast stations, from which this unit also came from.
Based on the not so stable Sony KSS-240a, but on the other hand, one of the better Sony KSS laser units that uses a motor/gear system for laser tracking. (I still prefer electro magnatic, like Philips’ swing arm or Sony KSS-151a linear tracking servo)
First impression, with the top cover removed:
Squeezed between the heavy duty pickup sledge and top cover/puck holder, there is the laser unit:
It appeared that the laser would not focus, or at least not focus well enough. Lets look a little further.
Laser units like the KSS240 have two electromagnatic servo’s with surrounding magnets. This way the lens can be pulled up and down by applying a small amount of voltage on those coils.
But that’s not all. By varying the current flow between both servos, it’s possible to move the lens also in horizontal direction, specially used for tracking because the motor/gear is slow and not accurate enough.
Because the focus lens was not moving very well, I tried to move it with a pair of tweezers. They should move very easily, but they didn’t.
I removed the black cap from the laser unit and discovered that some parts of the focus lens and servo got covered by a bit of stick glue. Using alcohol and a few cotton swabs I was able to remove this glue.
Where this glue came from is still unknown, I have never seen this before. After thorough cleaning all stickiness was gone and the focus lens was moving up and down like crazy. 🙂
A good and long test run and the Denon was good to go, so no need for a new laser unit.