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Old 29th November 2002, 03:18 PM   #21
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Hi,

There is some truth in Jean-Paul’s remarks. There is a small range of current the diode actually “lasers”. Below a threshold it will not laser at all and it is simply a LED and above a certain current level the laser will be destroyed.

Duo,

On most Sony’s there is a test point on the board labelled “RF”. It is near the connector where the cabling from the laser head enters the board. A “GND” point for hooking up the gnd lead of your probe is also nearby. There you will see the “HF eye pattern” as read from the disk. The nominal amplitude is 1 V_pp there for the Sony’s I have seen.

Good luck
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Old 29th November 2002, 03:34 PM   #22
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Okay, I'll try adjusting it by that. My scope doesn't have a setup for measuring voltage... Should I be able to use a vacuum tube voltmeter instead because of its super high impedance??? I guess I could feed a known 1vpp sig into the scope and mark where it shows up but that would be a bit of a pain...




Thanks
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Old 29th November 2002, 03:56 PM   #23
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Glad that there was some truth in what I said.
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Old 29th November 2002, 04:04 PM   #24
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Quote:
Should I be able to use a vacuum tube voltmeter instead because of its super high impedance???
Definitely NOT You must watch the peak to peak value on a scope. It is not a steady sine signal, although it looks somewhat to a sine. If you set the laser too high there is a serious risk of damaging the laser.
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I guess I could feed a known 1vpp sig into the scope and mark where it shows up but that would be a bit of a pain...
If your scope is not calibrated, this is the way to go then. But if the scale is accurate in V/div, reading the divisions on the screen is accurate enough. Oh, and your scope must be of at least 10 MHz BW.
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Old 29th November 2002, 04:36 PM   #25
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Okay, I see what you mean. My scope will do over 100Mhz so I know that's okay... Um, how can I make adjustments to this pot while the transport is operating??? Won't it be hard when the assembly is trying to move???
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Old 29th November 2002, 04:47 PM   #26
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Duo, it takes some experience but putting the player on its side with the cover off is common practice.
Some players have a dummy mode for adjusting the laser current.
Sometimes a jumper, sometimes you have to push a certain code on the panel for this.

Maybe obtaining a service manual will help ? It will tell you too how to adjust tracking and focus ( if applicable ).
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Old 29th November 2002, 05:28 PM   #27
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Good idea... Where do you think would be a good place to look for a service manual??

Any suggestions?
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Old 29th November 2002, 05:47 PM   #28
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I have a Sony CDP-910 (the same chasis is used on the CDP-222ESD and CDP-505ESD as well) that started skipping CDs. I got the service manual and went through the allignment proceedure and got things going again for a while. There was no mention of laser current adjustment, but the adjustment that was radically changed was the Focus Bias, all the way to one limit. After a few months the skipping started again and I put it aside for a long time. I just started playing with it again and initially could not get it to play anything. As an experiment I changed the resistors in the Focus Bias adjustment network to give a larger range of adjustment and I was able to get it palying CDs again. Sometimes it still take a couple of attempts for it to recognize some CDs.

I wonder if the focus bias could be your problem. To adjust the focus bias, hook your scope up to the RF test point and GND. In my case the adjustment pot is the one closest to the test point. Adjust for the best "eye" pattern.

I don't see any mention in my service manual about adjusting the laser diode current. Since this is a late '80s vintage model, I would not doubt that it could use a boost. Any thoughts on where the adjustment might be located?

I would also like to figure out what the root cause of my need for such a high level of Focus Bias is. Is there some link between laser diode output and focus? It doesn't seem likely. I did look at a book at an electronics store that indicated mechanical height adjustment of the disc over the optical pickup can affect the focus bias. This makes sense. Can this height creep over time? How would it be adjusted?
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Old 29th November 2002, 05:54 PM   #29
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Quote:
Originally posted by Duo
Good idea... Where do you think would be a good place to look for a service manual??

Any suggestions?
A Sony service center Or call Sony direct. They do sell them without any problems, at least here in Holland. They cost around $10,-

But the service manual will state: "Keep off the laser potentiometer" Probably for reasons already mentioned in this thread.
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Old 29th November 2002, 06:12 PM   #30
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Well, I'll see if I can get a manual then. I know what you mean about frying lasers with the current adjustment, I've fried many cd players with that pot not knowing exactly what it did... I guess I'll look into that focus adjustment too, that makes some sense as well. I heard that blue laser diodes are excellent in cd players, a friend of mine has a sony ES model of some sort with a blue laser diode in as a mod. His sounds very nice. I also have a CDP-CE505 here too but I don't use it simply because of the same problem my 305's been having. I hate unreliable equipment... Either way, I'll look into some more adjustments any how. THis thing isn't all that old so I don't see why I should retire it just yet. Heh, maybe the diode's burning out cause I use the darn thing 24/7 and have been since I got it a year ago.

I remember that when I got it, I could even give the transport fairly excessive shocks without any sort of skipping whatsoever. Now it's quite sensitive.
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