Which is the right direction to turn potentiometer on cd laser to incrase the laser power to increase the laser current

  • 2
    Participant count
  • Participants list

masterblaster1

CarAudio.com Recruit
55
4
Manitoba
Hi, My cd laser on my alpine 7903 cd player is on its way out,and just spitting out the disks, I can only get one original disk to play but it skips terribly bad. I am wanting to turn up the potentiometer a very tiny smidge say 15% turn to see if this will get the player to start accepting the disk,and playing them. I have already cleaned the laser eye, and relubed the rails. I want to try and adjust the potentiometer laser strnghth up a very small bit so I don't risk totally burning it out, But forgot what direction you are suposed to turn it to increase the laser output. Is it clockwise or counterclockwise. My memory says counterclockwise,But I thought I'd better check with all you experts here on this, And will it always be a certain direction to adjust it up, or does that depend on which cd player brand and model number you are using. Mine is the alpine 7903 that I'm adjusting now,But I would also like to try this with an alpine anniversary 7909 as well at a later time. Thanks in advance to all who chime in to answer this and for any advice to stop the alpine 7903MS from constantly ejecting the cds instead of playing them.
 
Hi, My cd laser on my alpine 7903 cd player is on its way out,and just spitting out the disks, I can only get one original disk to play but it skips terribly bad. I am wanting to turn up the potentiometer a very tiny smidge say 15% turn to see if this will get the player to start accepting the disk,and playing them. I have already cleaned the laser eye, and relubed the rails. I want to try and adjust the potentiometer laser strnghth up a very small bit so I don't risk totally burning it out, But forgot what direction you are suposed to turn it to increase the laser output. Is it clockwise or counterclockwise. My memory says counterclockwise,But I thought I'd better check with all you experts here on this, And will it always be a certain direction to adjust it up, or does that depend on which cd player brand and model number you are using. Mine is the alpine 7903 that I'm adjusting now,But I would also like to try this with an alpine anniversary 7909 as well at a later time. Thanks in advance to all who chime in to answer this and for any advice to stop the alpine 7903MS from constantly ejecting the cds instead of playing them.
Most laser circuits use an LM-317 adjustable voltage regulator. The adjust pin connects through the potentiometer to the resistance divider which raises the voltage the lower the trim value goes, so counter-clockwise = more voltage. If you're trying to make a small adjustment keep in mind that not all pots and circuits are created equally, so since you want to raise it by 15% presumably without a circuit diagram it's best to do this via voltage value between the + and - side of the laser diode itself, moving the pot very slowly. It should be apparent exactly where you want it based on the value it currently sits at + 15%. Cover the laser any time you power it without the enclosure, that'd be pretty dumb way to obtain vision damage.

I actually thought that CD players used digital trim pots that changed on the fly, but I guess you learn something new every day.
 
Thanks for your speedy reply, and your wealth of knowledge, I have none of the circuit value or even the voltage value. I was just going to put it all on the line, and turn it a very tiny small bit with the cd player having no power to it, and then reinstall it and see if the tiny counterclockwise turn of the potentiometer made any difference. This is a lot harder to experiment with car audio decks since it is buried deep in the deck, as compared to most home cd players which you can usually get at the potentiometer by just taking off the top cover.
 
Thanks for your speedy reply, and your wealth of knowledge, I have none of the circuit value or even the voltage value. I was just going to put it all on the line, and turn it a very tiny small bit with the cd player having no power to it, and then reinstall it and see if the tiny counterclockwise turn of the potentiometer made any difference. This is a lot harder to experiment with car audio decks since it is buried deep in the deck, as compared to most home cd players which you can usually get at the potentiometer by just taking off the top cover.
Probably the best step is to get it out of the riveted box if you're going to be experimenting on it as a lost cause. I would drill the rivet heads and get to probing with a multimeter, you're looking for the main laser diode voltage for your adjustment reading, but there's a lot that can go wrong with a laser reader. I don't necessarily think small adjustments to the power of the laser would help or hinder the read ability in most circumstances since they were calibrated to work from the factory. I have a variable DC power supply which has come in super useful, but in lou of that you can always use a car charger or 12-15v ac to dc power brick so you can do all your testing indoors. Head units don't use much power, like 200mA idle and 700mA during CD loading which is the peak. At least the few that I've had hooked up to equipment.
 
Last edited:
Hi, You have a lot of knowledge on this ,So thanks for sharing this with me. I like the idea of hooking it up indoors as well. This will save me a lot of time in the testing process,and testing it out when the tweak has been done. Wold still like a new laser for this unit or a good used one if this doesn't work though, Hopefully someone here has a few kicking around in their oldschool stock pile. Thanks for all your help so far.
 
Hi, You have a lot of knowledge on this ,So thanks for sharing this with me. I like the idea of hooking it up indoors as well. This will save me a lot of time in the testing process,and testing it out when the tweak has been done. Wold still like a new laser for this unit or a good used one if this doesn't work though, Hopefully someone here has a few kicking around in their oldschool stock pile. Thanks for all your help so far.
Not a problem. Once the chassis is off it should be pretty clear whether the laser is working. Most common issue is either a melted/dirty spot on the lens of the laser or the reader (usually the reader). In this case it can probably be picked off and cleaned with alcohol. The lenses are pretty tough compared to melted plastic. If it's not that then I'd say the laser diode going out is the second most likely thing. You can test that with a diode test on a standard multimeter while the unit is off. This will also help you determine the + and - side of the diode for measuring voltage off of if you do decide to screw around with the trim pot. If a diode dies it dies completely in almost every circumstance, so it'll either go open circuit or allow shorted current in both directions.
 
Thanks for the extra updated information on what I should be looking for and what I should be testing. I also see 2 settings on the actual circuit board that on my home cd player, when I turned them a little to the left or right made a difference in the cd player tracking to the song quicker,and tracking better in general.,and put a little mark on each of them first ,so I could turn them back to the original spot they were from the start. If things didn't go well. One of them when turned made it sound like it was clicking, So I dialed it back the other way. Will adjusting these be of any help when adjusting this car audio cd player.
 
Activity
No one is currently typing a reply...
Old Thread: Please note, there have been no replies in this thread for over 3 years!
Content in this thread may no longer be relevant.
Perhaps it would be better to start a new thread instead.

Similar threads

While we're speculating, why not bump up your volume gain (no pun intended) for just a few dollars more (literally) and go with the 8" versions of...
5
785
Hello, I already posted in general but wanted to also post in here. I recently installed a set of used JL audio shallow depth 12W 1v3-4 inside an...
0
654
Makes sense. You may be right on the gain; 2 subs on 300 watts seems anemic.
46
4K

About this thread

masterblaster1

CarAudio.com Recruit
Thread starter
masterblaster1
Joined
Location
Manitoba
Start date
Participants
Who Replied
Replies
6
Views
3,156
Last reply date
Last reply from
masterblaster1
Screenshot 2024-03-07 184329.png

Doxquzme

    Mar 27, 2024
  • 0
  • 0
IMG_3075.jpeg

Daniel Lee

    Mar 27, 2024
  • 0
  • 0

Latest topics

Top