Laser Diode current for KSS 151A? - Page 2 - diyAudio
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Old 25th October 2006, 04:35 PM   #11
anatech is offline anatech  Canada
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Hi beauty_divine,
I forgot to ask, what machine do you have?

The KSS-151A is a very nice head, a linear tracking motor design. Normally these go into some very nice CD players. Well worth repairing.

-Chris
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Old 25th October 2006, 04:48 PM   #12
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Thanks for the nice explanation
My CDP is Sony 338ESD.
May I conclude that the APC system with the ageing of the LD has to increase the Iop this way I can directly measure this increased current in order to judge the LD remaining life???
that is a bit stunning conclussion for me if I am right
Could you pass me a bit more info - what is written on a test CD that makes it being a test CD?
I tried to follow adj instruct. on an old harman/kardon incl. focus and tracking gain/bias with a good matrix CD and successfully completed all of them.
Or can I make a test CD by myself recording test tones in different tracks on CD-R or so?
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Old 25th October 2006, 05:50 PM   #13
anatech is offline anatech  Canada
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Hi beauty_divine,
Unfortunetly, you can not make your own test CD, they must be purchased. What makes a test CD is the pitch, eccentricity, reflectivity and pit shape. There are also manufactured defects on some involving all of the above attributes.
Quote:
May I conclude that the APC system with the ageing of the LD has to increase the Iop this way I can directly measure this increased current in order to judge the LD remaining life???
Yes, that is how it's done. LD life may vary, all you can tell is whether it's past it's useful life or not.

When adjusting focus and tracking gain, the proper test CD is very important. There are "ball park" methods that seem to work well. You are probably fine. The offsets and E-F balance adjustments are much more critical.

-Chris
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Old 25th October 2006, 07:11 PM   #14
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And now after I have moved the LD current trimmer position to get stable CD-R reading, how can I be able to restore the Iop setting to the previous, correct but unknown value?
Shall i try out the printed on the label Iop value +max 10% and see what will happen in time?...
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Old 25th October 2006, 07:12 PM   #15
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Quote:
Originally posted by beauty_divine

Hi Chris,
In general you are perfectly right, but what I had in mind was that I've got pretty old CDP and a new pick-up on hand. That is why I allowed myself to slightly touch the adj trimmer-just to squeeze little more life from the tired head.
What I still do not get after the discussion is how it is possible to have such great tolerances in the LD current and at the same time slight increase of it could ruin the laser? It seems controversal to me.

Hi

A laser hbehaves like a diode. the first say 50 mA run, but do not generate light. Than, at the bending of the power - current curve, the next mA generates about 1 mW of power. OPU's have a servo loop to control the power, as the bending of the curve also dependson the temperature.

best

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Old 25th October 2006, 08:03 PM   #16
anatech is offline anatech  Canada
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Hi beauty_divine,
Try setting your Ilaser to Iop + maybe 5%. With a precorded music CD you should be getting a sharp, clear eye pattern. I don't know what the expected amplitude is for your machine. Your laser current may even be close to the Iop value marked on the head. If you have the manual, they usually include a scope shot of the RF pattern. You can put the eye pattern close to that if your scope is in calibration, but less than the Iop + 10 % figure.

Try different discs and choose the one with the highest and clearest eye pattern to work with. You have a higher chance of needing a disc motor than a laser pickup.

Hi Guido,
Quote:
A laser hbehaves like a diode. the first say 50 mA run, but do not generate light. Than, at the bending of the power - current curve, the next mA generates about 1 mW of power. OPU's have a servo loop to control the power, as the bending of the curve also dependson the temperature.
That's a good explaination. Thanks, it may be clearer to some for sure.

-Chris
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Old 25th October 2006, 09:12 PM   #17
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Hi Chris,
I've got the service manual including the eye pattern and will try the measurement and settings you suggest but tomorrow as it is too late here already.
Thaks for the help again!

Good night!
Ivo
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Old 25th October 2006, 09:23 PM   #18
anatech is offline anatech  Canada
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Hi Ivo,
Good night and good luck tomorrow. Err on the side of caution.

-Chris
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Old 26th October 2006, 03:29 PM   #19
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Hi Chris, Guido!
1. I checked the Iop to find out that touching the adj trimmer has not created a disaster I measured 51,7mA vs 50,7mA printed on the paper label.
2. As I do not have a test CD to measure the eye pattern I did put an orignal matrix one to see that adjusting the corresponding trimmer could not increase the Vp-p above 1V. What I saw on the scope was that this amplitude depends on the disk type - pirated matrix copy or CD-R produce less amplitude.
In the service manual they recommend 1,3Vp-p +-0,3V. It seems I'm at the bottom line - even below. Could this be a sign for exhausted LD, or it is just because I do not use this test CD?
So far with these adj levels my 338ESD plays all matrix and CD-R CDs I have.
Thanks a lot for your valuable help and for the provided knowledge!
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Old 27th October 2006, 08:26 AM   #20
Salar is offline Salar  Germany
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BTW,
http://www.tohri.co.jp seems to be a good supplier for older laser units.
They are not specialised in that but still have some old units in stock.
Just checked for KSS-151A, they still got about 100 of them.
I bought three KSS-123A from Tohri three years ago, (I bought the last ones I guess) as far as I can remember, it was about 40 each, without tax.
A supplier here in germany charges 129...
All the best,
Salar
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