Getting a KSS-274A Laser into Ballpark

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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 don´t 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
 
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Hello Mooly,
I did. But I am wondering, why do I need a scope? When it is known how many µA are exactly needed to run the laser diode smooth and safely, all I need should be a voltmeter, isn´t 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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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.
 
Hello Mooly,
The laser power is adjusted optically at the factory.
How? Somebody once told me, photographs are taken from the pot´s position as reference for adjustement. Not very good, even if you hit the right "time"
variable resistors have play. That´s 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:
 
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!
 
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 £ 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

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.
 
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Hello Mooly,

How? Somebody once told me, photographs are taken from the pot´s position as reference for adjustement. Not very good, even if you hit the right "time"
variable resistors have play. That´s 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.
 
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.
 
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...
 
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You know, I've never seen laser factory photos, but it's a clear possibility, thinking about it, that the whole fixed pickup thing was based on the probably fixed pickup "player fixtures" that would seem to be required for proper adjustments on the KSS240 & such lasers. Some Sony exec touring the laser shop probably thought to himself, hey, that looks pretty cool, and would be a way to sell something new & high tech looking to put the idea into production players.

The whole perception of professional grade gear being built to a higher standard WAS true up until maybe the late 1960's, but in modern times, ALL it means is that the unit will have rack mounts & xlr connectors, and maybe heavier duty *looking* exterior hardware. NOTHING more than that. Just crack open, e.g., a Denon "pro" cd player, and you'll be clear about this.

I have managed to tweak the pots on KSS240's in pause mode. Very gently. Very rarely needs doing, though, and I have worked on hundreds of 240 based units.
 
I agree! Besides looking cool, the "fixed pickup" seems nonsense.
Thevintageknob claims that it was used in the very first professional
player "CDP/CDA-5000" available for studios and radio stations
before the CDP-101 was released.
I guess it was simply easier in 1982 to move a spindle motor
than to move a laser in the size of two cigarette boxes.
Still one question: The pot is connected to the monitor diode
not laser diode. Why?
 
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The whole perception of professional grade gear being built to a higher standard WAS true up until maybe the late 1960'

I don´t agree. It was more or less the late 1990´s because integrated circuitry
advanced so much, that you only needed some parts to build a complete player.

Ever opened a Pro BETACAM SP, camera or player? (late eighties to early nineties)

You know, I've never seen laser factory photos

So nobody knows for sure that individual alignment was made...

All the best,
Salar
 
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Laser current is critical. As you increase the current slowly in a laser diode it emits dull red light a bit like a side emitting LED. There is no lasing action. As the current increase there is suddenly a point at which lasing begins and from here, a very small increase in current causes a massive increase in the laser light emitted. Go to high and the facets of the laser diode are damaged and it just turns back into a dull LED.

Monitoring the eye pattern is the next best thing. The amplitude directly relates to laser power, however it doesn't allow for misaligned optics or dirty optics.

The bottom line is that the factory setting should not need altering.
 
Thanks. I mention it again: The original laser lasted only some estimated 6-7 years , whereas a KSS-123A lasers is playing for 24 years know.
And focus gain between original KSS-274A and the replacement is not the same.

But the fact that the KSS-123A laser in my Nakamichi OMS-5EII lasts for so long could have another reason: Nakamichi used a light barrier to detect the CD. When the tray is closed and a CD is not inserted, the laser will not be switched on.
But this appliance is missing in in the majority of players...
 
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One or two pickups are not statistically significant and in any case you would need to know the actual failure mechanism.

All players only power the laser when instructed to do so via the system control. The laser is not powered when there is no disc in the tray and /or the disc is present but the player is in stop mode.
 
Sony's pro video gear into the 90's was built very nicely, but so was the consumer level hi8, so not a lot of difference there. But Sony was an exception to the rule. Look at Panasonic or JVC's pro video gear at the time, and you find little more than the same low-end consumer dressed up as pro.
The laser current rating is absolutely useful as a "health indicator", only in conjunction with an optical power meter, as a like-new diode will output the proper optical power very close to that rating. This is actually essential way to measure on players like the first gen OMS5/7, where the NEC laser had to be within a certain current range for servo's to work right, but the laser had a habit of needing quite a lot more than spec to output enough light.
The primary reason, in my view, that lasers like the KSS123 have had such very long lives is that they were a LOT more robust laser diodes. They were designed to ouput 0.24mW, rather than the 0.1-0.15mW of all lasers, from pretty much all makers, from the KSS150 era forward. The photo-interrupter disc detect on the Naks had little to do with it, judging by how very few 123 and similar Sony lasers I've ever needed to replace in lots of other makes/models.
 
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