CD-ROM Electronics Question...

My CD ROM was having trouble reading CD's for a while, and hardly ever got better after cleaning, so after a bit of poking around in it, I found a little circuit with a tiny 'pot' situated on the lens mounting, it was connected directly to the laser diode, so I gave it a twiddle to increase the diode output and my CD works fine now. I just wondered what the pot is called in this circuit? (like LD-gain or something).

I'm asking this because it appears to be an overlooked problem with a very easy solution. My friends CD player stopped reading all CD's and they sent it away to be fixed a total of 3 times, each time it was sent back the repairman saying "It's working fine.". In the end he gave it me to strip down, but instead I had a look to see if I could find the problem. Even without using any test equipment, I located this potential devider and gave it a twiddle. I now have a fully working music system! If it's happened to me twice, how many other people has it happened to? There must be hundreds if not thousands of discarded CD-ROMS all because of a miss-set pot.
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The pot undoubtedly controls the LD output level and is probably adjusted at the factory to produce a specific readout level with a test disk for a particular S/N (signal/noise) ratio.  If the level is too low, there won't be enough signal for the detection to work reliably.  If the level is too high, the detctor will be overwhelmed and unable to distinguish between "0" and "1".

I see nothing wrong with "treaking" it as it's not working anyway and you can't make is any worse.  My guess is that the "tech" who sent it back as OK, never did anything but plug it in and see that a disk worked.

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Well I have found those cleaning disks next to useless, I have had a couple go like this myself, but on srtipping them noticed the lens was filmed and dirty, this after repeated applications of a cleaning disk, so cleaned it with a q-tip (cotton bud in UK) and alcohol and they worked great again, so maybe you just turned it up just enough to see through the murk.

Ummm, erased any CD-Rs with it yet?   ;-)

Road Warrior
Lab_RatAuthor Commented:
Good point, RW! I'll have a go tonight, and if it works I might start up a disc blanking business!
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