Getting a KSS-274A Laser into Ballpark - diyAudio
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Old 15th August 2014, 01:57 PM   #1
Salar is offline Salar  Germany
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Default Perfect Adjustment of KSS-274A Laser Power

Hi to all,
I replaced the laser of my CDP-X5000, a KSS-274A. Everything works fine, but something bothers me:
I used the player not very often, I own it for 17 years, used it for maybe six years. Not a very long time to weaken a laser diode, a KSS-123A based player of mine - a Nakamichi - did not need an replacement after 20 years of daily use.

The replacement laser KSS-274A came already aligned from the factory.
There are variable SMD resistor pots for E-F Balance, Focus Gain, Laser Power. But the new laser hisses more than the old one, a sign that the Focus gain on the replacement is cranked up. So I guess there is some play in adjustment and I donīt trust SONY that adjustement were made perfect in the factory.

I would like to check the alignments myself.

In the service manual no servicing routines are described at all besides changing the laser an aligning the distance to a CD with a screw.
Amplitute of Eyepattern can be checked fore Laser power, thats all.

But my scope is not very reliable.

Are there any other ways to check the laser power maybe using a voltmeter?

It is a fixed pickup, so no problems with that...
All the best,
Salar

Last edited by Salar; 15th August 2014 at 03:40 PM.
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Old 15th August 2014, 05:52 PM   #2
Mooly is offline Mooly  United Kingdom
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You have probably come across this thread but it if not then it covers general alignment. The adjustments all work in the same way on any player. And yes, you need a scope.

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Old 15th August 2014, 06:15 PM   #3
Salar is offline Salar  Germany
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Hello Mooly,
I did. But I am wondering, why do I need a scope? When it is known how many ĩA are exactly needed to run the laser diode smooth and safely, all I need should be a voltmeter, isnīt it?

Again, the player works just fine. But I want the diode to run within the best (safest) parameters because I assume that factory alignment is coarse.
All the best,
Salar
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Old 15th August 2014, 06:36 PM   #4
Mooly is offline Mooly  United Kingdom
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The laser power is adjusted optically at the factory. You have to take it that that setting is correct. Easy confirmation comes from checking the RF signal from the disc.

Everything works together and effects everything else...

Its possible to have correct optical output but see a low RF if the cause is say a dirty lens or internal optics or misaligned focus servo. If the RF is good and high in amplitude then you can reduce the laser power which would increase its life, however, the laser diode is conservatively rated and you'll have scrapped the player long before the diode losses efficiency.

The laser current used to be marked on the pickup as part of the serial number, whether that applies on the KSS274 I don't know. And to check, you need to look at the laser drive circuitry and identify the correct resistor to measure across. Even worse, the action of poking a meter on the resistor must be done carefully by wiring it all up first because even the slightest and briefest current spike (we are talking nano and pico seconds) can degrade the facets of the laser and cause premature failure.

You need a scope to work on CD players I'm afraid, no other way. It tells most if not all.
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Old 16th August 2014, 12:41 PM   #5
Salar is offline Salar  Germany
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Hello Mooly,
Quote:
The laser power is adjusted optically at the factory.
How? Somebody once told me, photographs are taken from the potīs position as reference for adjustement. Not very good, even if you hit the right "time"
variable resistors have play. Thatīs why i do always change resistors to multiturn trimmers for adjustment.

But watching the circiut diagram, I see that the monitor diode is being biased by the pot, not the laser diode itself. Why?

But something else strikes me: I took the circuit diagram of the KSS-240A to compare to the KSS-274A - and they are identical!
Maybe this means that the same diodes are used?
Imagine - the KSS-274A are long gone, the KSS-240 are still available.
I started a new thread about this:
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Old 16th August 2014, 12:50 PM   #6
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Squealing is caused by high Focus Gain and the Focus coils, like a speech coil, resonating.
You need to check the lucidious waveform if a minor reduction in Focus Gain doesn't fix your issue.
Whatever you do, unless you own a laser power meter, attempt to adjust the laser power. You will reduce the useful life of the diode.
I would personally trust a major manufacturer to get pretty damn close!
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Old 16th August 2014, 01:53 PM   #7
Salar is offline Salar  Germany
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Hello Jon!
Thank you very much, but this thread not so much about general setup or a
the bothering hiss.
The squealing / hiss is normal, I remember when a friend got his KSS-123A based Denon player repaired back in 1986, he also complained about a loud hiss afterwards. The hiss can also be reduced by ear without compromising tracking.
No, this thread is just about having the laser diode run at the sweetest spot according to longetivety. With my experiences alone with this High-End player CDP-X5000, worth Ģ 850 back in 1997 I do not trust Sony at allthat they saved some bucks in aligning and did it not as proper as they could have done. The other problems with this player were:
VFD segments fading faster over time than usual, the famous "Fixed Pickup Mechanism" made from plastic, RCA sockets you suddenly hold in your hand because the ground ring is not soldered to the pcb and probably wrong resistors having the mechanism skip.
Also there was problems in making the player start after the lid was closed, again caused by a wrong resistor.

Anyway, because electronically the KSS-274A does not seem to differ from the KSS-240A, I started this thread

Quote:
however, the laser diode is conservatively rated and you'll have scrapped the player long before the diode losses efficiency.
Please proof that the laser diode is conservatively rated. Scrapping a player is not very easy. Besides defunct Laser Units, many parts are still available. I.e. Sony and Phillips used / use motors from Mabuchi
like the RF-310TA-11400. My Sony-based Nakamichi Player from 1986 has this motor - and it is still available.

Last edited by Salar; 16th August 2014 at 02:16 PM.
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Old 16th August 2014, 03:48 PM   #8
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by Salar View Post
Hello Mooly,

How? Somebody once told me, photographs are taken from the potīs position as reference for adjustement. Not very good, even if you hit the right "time"
variable resistors have play. Thatīs why i do always change resistors to multiturn trimmers for adjustment.

But watching the circiut diagram, I see that the monitor diode is being biased by the pot, not the laser diode itself. Why?

But something else strikes me: I took the circuit diagram of the KSS-240A to compare to the KSS-274A - and they are identical!
Maybe this means that the same diodes are used?
Imagine - the KSS-274A are long gone, the KSS-240 are still available.
I started a new thread about this:
They are adjusted optically with a laser power meter. The photo diode output forms part of a servo system, the higher the laser light output and the more the photodiode output. That increased output acts on the laser drive amp by reducing the current. The pot just allows for a user control to set the laser diode at the correct value by modifying the photo diode output. The tolerances of the laser diodes are far to wide to not have any manual control.

Wouldn't like to say if they were the same diodes or not tbh.
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Old 16th August 2014, 09:02 PM   #9
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I have never seen a KSS240, 274 or similar with misadjusted laser output from the factory. But agree that it should NOT be adjusted without an optical laser power meter, because you really can't count on any current designation on the laser being totally accurate(from practical experience). As for the focus servo, it IS possible to get gain & bias pretty close to ideal without a scope. Sony often sets gain too high, and tracking is better with it lower. I would adjust so hiss is audible only within a foot distance with lid off, i.e., pretty quiet. Then adjust focus bias(offset) to minimum hiss level. This should put the servo pretty damn close to optimum.
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Old 16th August 2014, 10:28 PM   #10
Salar is offline Salar  Germany
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Thanks for the answers. Just to make things clear:

Every laser leaving the assembly line was individually adjusted using a laser power meter - despite the fact that it must have been thousands of them leaving the assembly line each day?
I do not know how much automation had advanced twenty years ago, but I doubt that it was done automatically.
If this was really done by hand, this must have been horrible job for the workers. Look at the small pots!
And laser power does not rise/decline linear.
Where to get the time, calm and and comfort to adjust them?

Someone explained to me that this is why professional equipment (I work as an editor) is much more expensive, not only because of lesser units but also because of
individual quality control and adjustment at the factory. Consumer equipment is cheaper, because quality control is based on samples, one each 500 or 1000 units. If the sample is good,
the batch is regarded as being good as well.

EF-balance and focus gain of the KSS-274A left the assembly line pre-adjusted, but the focus gain of my replacement laser is higher (more hiss).
At least this adjustment differs.
With the KSS-274A, a service technician could align these pots, because the laser is fixed and the disc is moved.
But this is not described in the service manual, only measurement and the advice to replace the laser when measurements differ.

With other "ordinary" lasers ( 99,9% are not "Fixed Pickup Mechanisms") which have the RF-Amp and pots on-board, you can not align anything.
Only when the RF-amp is on the main pcb...

Last edited by Salar; 16th August 2014 at 10:44 PM.
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