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Old 19th September 2010, 07:17 AM   #11
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Without measuring with an optical laser power meter, it's impossible to tell for sure. But, considering that it should have been able, as far as I know about that laser, to play cd-r's in the first place, it's probably within tolerable range of normal output now. So, probably be ok for years.
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Old 19th September 2010, 07:20 AM   #12
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How does the RF compare with CDR to ordinary CD ? and by how much has the amplitude of the signal increased now you have altered the power ?

As to the laser... hard to say without hard facts.
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Old 19th September 2010, 07:29 AM   #13
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Well, I was very specific about adjusting the pot. I made sure it's not powered up and made super small incremental adjustents. Based on the amplitude of the RF pattern using the same CD as reference, I can tell I had to increase the laser power by 20%. In this player, the RF amplitude needs to be around 2V minimum for it to work. Looking at the datasheet for the LA9200, I'm wondering if a more wise approach wouldn't be for me to increase the gain fro the RF amplifier? It get's set with two resistors, so should be easy enough just to try.

RF output is less than for normal CDs. I also don't see the same definition of the eye pattern between pressed and CD-R's. I suppose it's to be expected.
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Old 19th September 2010, 07:52 AM   #14
Mooly is offline Mooly  United Kingdom
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The problem with increasing gain is that you increase the noise too... without having the player in front of me I wouldn't like to advise on that.

I'm not familiar with that laser pickup either... in that I don't know whether any adjustments need to be made on the pickup itself following replacement, such as diffraction grating adjustment etc, or any mechanical alignment procedure. That can and does have a huge impact on the quality of the signal recovered.

Edit, post number 9
NAD C540 CD Player No Disc

is about another player and CDR compatability. If you gathered all the info and circuits maybe you could see what areas of the player were modified and what the changes achieved.

On the laser again... when the laser power is adjusted during manufacture, then that's an optical adjustment using a power meter. As the current is increased the laser operates initially almost like a side emmiting LED, then suddenly at a given current lasing action begins, and a very small increase in current gives a large increase in the laser output... this is why it has to be so carefully controlled with the APC (Auto power circuit).
That pre-set current is then correct to give the required RF output from a CD but only if all the mechanical and electrical alignment is correct. If there is a problem there, then the output will be "low" even though the laser power is actually correct, so turning up the power is "fiddling" the issue.

I'm not saying that's what has happened here, just something to be aware of.
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Last edited by Mooly; 19th September 2010 at 08:03 AM.
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Old 19th September 2010, 06:32 PM   #15
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I know those Sanyo lasers well enough to say that there definitely is no post-manufacture adjustment of diffraction grating possible, and they are well locked. I can also say that this one is old enough that it's laser diode was almost certainly the sort to have a spec of 0.24mW output, and will tolerate easily 0.28mW constant without degraded life. But I can also say that, given the servo adjustments all checked out ok, it would definitely play cd-r at rated output, so is almost certainly close enough to that to be fine. Were it a later laser with 0.1-0.15mW constant rating, it would be a different story, depending on model. But the 0.24mW lasers have more range of safe operation, usually.
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