Laser Diode current for KSS 151A?

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#22
Those heads were very expensive when new. I can understand a vendor trying to recoup their money. I think Nakamichi list was $450 ~ 550. CDN or something while new. There was an NEC head that was much more expensive used in the Nak OMS-5/7, Also in the first Alpine CD player. That was a wonderful head. I did buy one new from Nakamichi, the memory stings but I'm still using the player (OMS-7).

-Chris
 
#23
I think I bought the last 30 laser units from Japan two years ago. I can't remember who the vendor is but I still have 10 left and I am selling them for $85 here in the US. These are brand new in box and never opened. I used them in alot of mid-high end Denon DCD-2560, DCD-3520 and DCD-3560. These are the same ones that go inside high end Sony players as well.

The same laser is sold here in the us but it costs about $130 after tax and shipping cost.

Installation is not easy as you have to take apart the whole mechanism and some soldering.

Good luck!
 
#26
#27
tiefbassuebertr said:
are there any news?
Click to expand...
Yes, there are some news I would like to share 😉
After I found my old CDP Sony 338ESD (employing the KSS-151A) under a layer of dust but still alive I checked the old thread for details on how to estimate the condition and remaining live of the laser pick up unit.
Before to play with the Iop measurements I came across the attached part of some kind of a service manual.
I did wait for the player to warm up and measured Iop=52.8mA (the factory set Iop=50.7mA according to the printed label). Then played a little bit with the trimmer for Iop adjustment for lowering the current down to the threshold not to accept CDs and turned it back just a bit. No matter how much I decreased the initial Iop after around 10 minutes of warming up the LD the Iop settles up to 52.8mA 🙂 It means the auto power regulation system sets the necessary current for the needed laser beam power. After 22 years of operation (the CDP is dated back to 1991) the Iop current has an increase of 2 mA for keeping the beam power. According to the attached file I still have some 8mA to go before to consider the pick up for replacement if still any remained in the world at that moment of time... 🙁
BTW I tried to look for unused (spare) KSS151A and crashed. The parts selling companies say it's discontinued along time ago. On ebay there are only used parts with unknown condition but shamelessly priced...
 

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#28
The exact figure will depend on temperature too. Unless you match the (unknown) factory temp then the readings are bound to be a little a different. The laser power preset doesn't hold the current constant but rather the optical output from the laser diode as I think you realise.
 
#29
I don't know but I really want to believe that in the factory, before the adjustment of Iop for the right output, they had given enough time to the laser to reach nominal working temperature and then to adjust Iop. In this case my readings and the factory readings should have good correlation.
And yes, the optical output is to be kept constant but with aging this is by the cost of higher current as a sign of exhaustion. So far I did not know how much mA in excess was the threshold for faulty unit. Now the manual for KSS151A says Iop+10mA

P.S. On top of everything in my CDP the 22 Ohm current sensing resistor is 5% tolerance. 5% of 50mA are some 2.5mA error 🙁
 
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#30
I don't think you have anything to worry over with regard to the laser diode.

All you could realistically do as an experiment is cool the unit to say 15C and measure the current, and then compare it to the value after the player has been running for a couple of hours. Now you have adjusted the trimmer the exact original setting is lost anyway.
 
#31
Mooly said:
All you could realistically do as an experiment is cool the unit to say 15C and measure the current, and then compare it to the value after the player has been running for a couple of hours. Now you have adjusted the trimmer the exact original setting is lost anyway.
Click to expand...
I had some thoughts to do that kind of experiment but I'm doubting what might be the use of the possible result. Even now (in my basement shack) the temp is 20 C and the start up Iop is down to 50mA as on the printed label. The LD needs only 10 minutes to reach stable temp and Iop is ~53 mA and does not increase any more. The theory works so what?
And having the original trimmer position lost does not bother me a lot as it gave me a couple of hours of nice play 🙂
 
#32
It all sounds normal. The factory setting will be done at room temperature. They won't wait for it to stabilise temperature wise because there is no need. Time costs money too. So its powered up, optical output monitored and pot set as required... takes seconds... and that will be the value printed on the pickup.

Don't worry, it will be essentially the same now as when it was new 🙂
 
#33
Nevertheless I considered it pointless I still measured the Iop after 2 hours of work and registered 54mA@28 C in my room (quite hot this Summer here 😉 )
Finally: after 10 minutes of work Iop=53mA @Tamb.=20 C and after 2 hours Iop=54mA @Tamb.=28 C.
I guess this has become exhaustive report on how the KSS151A behaves after 21 years of service. There was another topic in the forum where the author expressed his disappointment of this Sony optical pick up. My figures say exactly the opposite.
 
#34
Actual failure of a pickup can be down to many things, mechanical lens suspension problems, lens bearing problems (sticking) and electrical issues such as leaky photodiode arrays. And of course a build up of contaminants on the internal optical surfaces. I think the laser diodes themselves are generally fairly reliable.

Enjoy the player 🙂
 
#35
Allow me to post a picture of a rare beauty I came across. It is not taken from an old vintage machine but from a dusty shelf in a service repair company. I'm still very happy by this rare chance. What makes me curious is the following. In my CDP the Iop=50.7mA. On the label of this pick up Iop=50.0mA. It is quite low value compared to the pictures of the KSS151A generally on ebay whose Iop is around 75mA. I was wondering whether the low Iop value correlates to a possible larger lifespan (due to lower working temp.) and the other way around - the higher the Iop - the lower the life span because of the higher current and working temp? Could this Iop value be a relative sign to choose a better pickup?
 
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#37
Wouldn't like to say tbh. Different laser diode from different manufacturer maybe, or maybe devices at the end of the acceptable characteristics curve. Ultimately the chosen iop is the value needed to get the required optical output.
 
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