the laser voltage drops

[kaulagalvis]

hello,problem with cdm2 Player play about 4 tracks and stoped.Chek laser voltage 50mv and when it play,voltage go down and stopped when it is 19mv.
I have this problem in some philips players with cdm2 and cdm4 ,replace chips and eletrolytics caps,lasers but its the same.Can you help me?

 

[Mooly]

I have had a couple of cases of intermittent failure of the laser diode drive transistor on the servo board in the past. Make sure you have replaced the electrolytic that connects to the base of this transistor.

 

[markos4553]

I had this issue with a cdm-4 in a Rotel RCD 855. It ended up being a bad laser monitor diode in the array which is not fixable. The fix was swapping a compatible swing arm with working laser in.

Mark K.

 

[kaulagalvis]

I have had a couple of cases of intermittent failure of the laser diode drive transistor on the servo board in the past. Make sure you have replaced the electrolytic that connects to the base of this transistor.

Thank you for answer ,of course I replaced electrolytics in first.,but its not help.

 

[kaulagalvis]

I had this issue with a cdm-4 in a Rotel RCD 855. It ended up being a bad laser monitor diode in the array which is not fixable. The fix was swapping a compatible swing arm with working laser in.

Mark K.

Thank you.Where is laser monitor diode?Laser working well in other player.

 

[Mooly]

Try changing the transistor then. Its only a small signal BCxxx type. Has to be worth a try.

 

[kaulagalvis]

ok.many thanks!

 

[kaulagalvis]

its not help.laser voltage about 17-18 mv in all pot s pozicions and go down

 

[Mooly]

Next step would be to look at the laser current by monitoring the volt drop across the low value resistor that is connected to the drive transistor (sorry, haven't got the circuit in front of me) and see if it drops or not. Also look at the drive voltage to the transistor.

Freezer spray used very sparingly on and around the chip controlling laser power might be useful.