During my career, I have replaced hundreds of defective laser pickups.
Whilst some have emitted no laser light, the vast majority do emit light but will not work correctly.
In these cases, the cdp may load TOC, but then not play, or will load TOC and play, but mistrack easily on various discs or when the player is bumped.
Examination of the HF waveform reveals dirty signal in some cases, but not all.
Any references to a definative study of what causes laser pickup assy failure ?
Eric.
Whilst some have emitted no laser light, the vast majority do emit light but will not work correctly.
In these cases, the cdp may load TOC, but then not play, or will load TOC and play, but mistrack easily on various discs or when the player is bumped.
Examination of the HF waveform reveals dirty signal in some cases, but not all.
Any references to a definative study of what causes laser pickup assy failure ?
Eric.
Laser Failure
Hi Eric,
Never agreed more with a post. This laserfailure is a tricky business.
Very often the eyepattern looks OK on the scope but the player mistracks and skips. The only thing I could see is that the amplitude goes down but that is also not always clear.
We crancked up the output of some lasers to help the custumer but these came back in a few weeks, then claiming warrenty!. Never do that again. A built in servicehour counter would be a nice thing.
Hi Eric,
Never agreed more with a post. This laserfailure is a tricky business.
Very often the eyepattern looks OK on the scope but the player mistracks and skips. The only thing I could see is that the amplitude goes down but that is also not always clear.
We crancked up the output of some lasers to help the custumer but these came back in a few weeks, then claiming warrenty!. Never do that again. A built in servicehour counter would be a nice thing.
All solid state laser diodes do wear out after an amount of service time. In the laser cavity of the diode will come very tiny cracks after time. When there are sufficient cracks there is insufficient “Lasering” left. Also the light output of the LED exiting the laser cavity will drop after time. This you can see at a too low EFM signal.
I cranked up the laser of my Sony CD player when it started skipping and served me another 4 years. But that is luck. Most time the laser is definitely gone within a year or so after such an adjustment. It is always best to replace the complete laser head in such cases.
I cranked up the laser of my Sony CD player when it started skipping and served me another 4 years. But that is luck. Most time the laser is definitely gone within a year or so after such an adjustment. It is always best to replace the complete laser head in such cases.
When we measure the RF and all looks ok, we take out the axe, clean it with methanol and lubricate it again. In many cases the axe is also the reason of failures. The spindle motor is sometimes a problem too. In some old Pioneer's we replaced it together with the lens. In some Sony drives we always replace the small flat cable as well. If possible I replace the whole drive. As an example, I can by the KSS213C laser unit + drive cheaper than the laser unit without drive. But, as stated, they can be tricky.
Hugo
Hugo
Re: Laser diode replacement
http://www.blackpudding.fsnet.co.uk/digital_jitter/philips_laser.htm is a good reference site for everything about lasers.
/Hugo
diyman said:
http://www.blackpudding.fsnet.co.uk/digital_jitter/philips_laser.htm is a good reference site for everything about lasers.
/Hugo
Exact this I observe in the meantime often on Philips CDM2 and CDM4 laser units (HF resp. eye-pattern signal with correct magnitude according service manual, but with a high level of noise - i. e. dirty HF signal like here under
https://www.domesday86.com/?page_id=2678 - yellow diagram).
Consequence is, that some (not all) compact disc sounds like a dusty stylus on a record player cartridge - especially burned versions.
For me looks this diagram perfect:
https://commons.wikimedia.org/wiki/File:Cdeye_en.png
The question for me is, which part of the follow mentioned is the reason for unwanted noise in most cases:
1) Laserdiode (if it is possible that also noise can be generated by this part without lower emission)
2) Guard ring photo diodes (if noise can be generated by this part)
3) integrated HF/RF signal amplifier section of TDA5708 or KSS-240 with noise
4) Automatic Power Control (APC-) unit (hard to believe for me, that noise occurs here)
Any experiences ? Thank you very much for any advice.
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The suspension carrying the lense sometimes will sag and move the focus center offset to the point it can't move enough downwards, away from the disc to focus cleanly. This is common on 3 beam Sony transports. Another is lens contamination on the backside of the lense or one way prism. If you have any outgassing vapors or chemical residue that migrates onto the back of th lense, the PU asy is usually a gonner since you can't get to that surface to clean it.
I've seen:
Laser power fail
Fungus in lens
Lens lost due bad glue(Pioneer laser pickups)
Dirty in lens
Photodiode Array sensitivity lost.
Mechanical maladjustment, above all moving lens.
Potentiometer in laser pickup maladjustment, due to resistor value drift.
Etc... etc... etc...