I am working on a CD player built around the Phillips/Magnavox chassis typical of the CD150. It uses the CDM2/10 laser assembly.
For the most part it is functional and it operates similar to identical units I have.
This unit however will only play CDR's. If I put in a store-bought CD it will not even read the TOC. That is something completely new to me. I have seen functional CD players refuse CDR's but rarely refuse an original pressing.
I cleaned the lens and adjusted the laser operating current to 51mv (50mv +/-5mv per CDM2 service manual ).
Could one of you offer a tip on how to proceed?
For the most part it is functional and it operates similar to identical units I have.
This unit however will only play CDR's. If I put in a store-bought CD it will not even read the TOC. That is something completely new to me. I have seen functional CD players refuse CDR's but rarely refuse an original pressing.
I cleaned the lens and adjusted the laser operating current to 51mv (50mv +/-5mv per CDM2 service manual ).
Could one of you offer a tip on how to proceed?
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I have two other units of the same model that plays the CD's in question just fine. I just tried it again to be sure. The CD is a "Best Of Run DMC" title. Surface of CD is impeccable.
I don't keep a lot of CD's by my workbench so I grabbed a bunch of others.
Lets call the problem player "Unit 1"
Lets call the backup player "Unit 2"
Both are the exact same model but produced one year apart.
Depeche Mode has small surface scratches. Does not play in Unit 1 but will play in Unit 2.
Pink Floyd plays in both.
Best of Run DMC has perfect finish. Does not play in Unit 1 but will play in Unit 2.
Red Hot Chili Peppers plays in both.
CDR's play in both with ease which is what surprises me the most.
So is it possible that I may have to push the laser current up a little further on the trouble unit? My experience in this is limited and I don't want to push the laser diode too hard if unnecessary.
The Run DMC CD is 56:35 in length.
I did notice something I have never noticed before though.
This is a CD I probably picked up from a clearance bin for $1.99 at Best Buy.
In small print on the back of the jewel case it states this CD has some kind of bonus material and MP3 ready files in it somewhere. I popped it into my PC and sure enough it shows up as some type of "Enhanced CD" so it is probably not following Red-Book standards (probably Orange-Book).
So that may be the problem with these 1987 era players. I tried about 6 store bought titles in both units and the Run DMC and Depeche Mode were the only that did not read TOC. I can't explain why it would play in one of two CD players of the exact same model though. I will say that even though they are the same model, both units have different main boards and one has a SPDIF output. Maybe the newer main board knows to ignore the hybrid disc?
The Depeche Mode disc is old and a bare-bones Red-Book CD. It has some signs of wear but still only plays in one of the two units.
The '50mv' Philips method of setting laser power relies 100% on the reflectivity of the discs. You are actually measuring the total combined photo diode array current (measuring the volt drop across a resistor) rather than looking at anything disc independent.
It is always best practice to look at the RF on a scope and see what kind of amplitude you actually have.
A CDR should not be used for the official setting method.
Despite the odd symptoms the usual troublesome caps should be replaced as a matter of course.
An 'enhanced CD' should be playable in any normal player although some have been known to misinterpret the data sections and not mute the audio feed if they are attempting to play the data section.
It is always best practice to look at the RF on a scope and see what kind of amplitude you actually have.
A CDR should not be used for the official setting method.
Despite the odd symptoms the usual troublesome caps should be replaced as a matter of course.
An 'enhanced CD' should be playable in any normal player although some have been known to misinterpret the data sections and not mute the audio feed if they are attempting to play the data section.
Thank you. Yeah I kinda thought that 50mv thing was a good baseline to start but I can wholeheartedly understand that cranking the laser current up can't help a scenario where the detector is weak.
So I have one last question. These particular laser assemblies look like they are robust and also look like they can be taken apart. Is that an exercise in futility? Is there any point in trying to see if the interior of the laser is dirty or has a film in it? Since I can get a variety of discs to play on this unit I will probably leave it alone but this is something I would like to know for future reference.