PowerBook G4 (finally) reads cheap CD-Rs

[PowerPup]

More of a hardware "repair" than a hack. I was getting tired of how my cheap Philips CD-Rs just wouldn't work in my PowerBook G4 no matter what speed I burned them. So it got me thinking, the reason why game consoles (esp. GameCubes) often stop reading discs is because the laser's POT (resistance) is either too high or too low. Thus making the laser too weak or too strong to read the disc. (This happens due to age/wear, improper calibration or both.)

I noticed that these Philips discs are extremely transparent compared to other CD-Rs. (I'll add a comparison pic later.) Because the label's side coat was so thin, I assumed the laser was so strong that it was just shooting pass the disc.

So I cracked open my PBG4 and opened the lid off the DVD/CD-RW combo drive, quickly locating the pot on the side of the laser mechanism. Taking my multimeter I found out the resistance was set at 150-Ohms. So I kept increasing the resistance (thus reducing the strength of the laser) in increments of 30-50 until it was reading the Philips discs perfectly every time. (Double the original setting, about 300-Ohms. This also happens to be around the "sweet-spot" for GCs.)

So by lowering the strength of the laser not only have I gained the ability to read cheaper discs, but it'll likely extend the life span of the drive as I'm not burning out the laser as quickly. (I've also tested DVD videos in it and they still work fine.)

Note: This is only testimony of my personal experience and in no way am I an expert on the matter. Use this technique at your own risk!

 

[techknight]

You sure increasing the pot resistance is actually lowering the laser power? in some cases it can increase the power. it depends on how the circuit is designed.

 

[PowerPup]

Good point, though I haven't come across any references yet suggesting so.

http://team-xecuter.com/forums/showthread.php?t=61768

So what we are doing by decreasing the resistance of current flow to the laser diode, is basically increasing the lasers power. thus making it easier for the laser beam created by the diode to be focused by the laser lens and be reflected back so it can be read by the assemblies optical sensor.

http://forums.cvxgameconsolerepair.com/phpbb/viewtopic.php?f=5&t=196

The purpose of a pot tweak is to decrease the laser's resistance settings in order to 'increase' the current to the laser diode itself and therefore making it 'stronger'. As a result, this 'will' decrease the lifespan of your laser, and you should not be doing this unless the laser is currently not reading the 3 media types.

So while its always possible that the combo drive in my laptop may have a different circuit design, a manufacture inverting the function of a resistor on something as standardized as an optical drive seems illogical to me. (But then again, humans are renown for doing the illogical. ) )

If you have any suggestions on how to confirm it do let me know.

 

[techknight]

Your referring to links about game consoles/xboxes. I work on those every day and decreasing the resistance increases the laser output power, so your argument would be valid that increasing the resistance is dropping the power.

But I also have seen some designs that do the exact opposite, this is dependent on the laser power output design. Also I have seen old school CD players that dont use a pot at all, it uses automatic power regulation based on optical feedback.

 

[PowerPup]

Well maybe I'll get lucky and find the service manual or something for the combo drive. (Going to have to open the laptop back up as I can't remember the brand.)