I think so. It will be the preset closet to the laser diode itself. The last three digits of the pickup serial number should be the factory set laser current, for example ending in 593 would be 59.3 milliamps calculated from the volt drop across the emitter resistor of the laser diode regulator transistor.
Thanks for the info Mooly. I'll soon try to turn the potentiometer and read the laser voltage with an oscilloscope. 1.2V/(22)Ohm = 54.5mA laser current,
so it should be something.... HF = 1.2V is probably new. Laser voltage at 800mV, less current will flow through the laser diode,
I will increase it to 1.2V and see if CDs can be read well.
so it should be something.... HF = 1.2V is probably new. Laser voltage at 800mV, less current will flow through the laser diode,
I will increase it to 1.2V and see if CDs can be read well.
I just turned the pot left and right, it's very difficult to get to it because it's installed at an angle. And no, nothing has changed. HF remains at 800mV.
The marked red 1 potentiometer must have a different function. I have little experience with expanding the KSS272A. Those who have experience with Sony cdp x339 should write. Maybe you can't adjust the laser current on this model?
The marked red 1 potentiometer must have a different function. I have little experience with expanding the KSS272A. Those who have experience with Sony cdp x339 should write. Maybe you can't adjust the laser current on this model?
Not everything about the KSS272A is recorded in the Sony Servicecircuit diagram CDP-X339. I found other KSS272A PDF. It seems to be an automatic laser current control. APC 2.2k there is a control. Can be seen below in the circuit diagram. Yesterday I turned the TB tracking bias potentiometer. I thought it was the laser current potentiometer, but it wasn't. At the moment it's running again since I turned on the TB tracking potentiometer I turned. I noticed the position. I'll leave it like that for now Greetings Chris
The APC circuit is similar in any pickup with the optical power of the laser being held constant at a level determined by the preset adjustment. The current is varied to achieve this constant optical output and that is why the actual current is such a good guide to the laser condition and why it marked on each pickup via the serial number. If the current is higher by 10% or more then the laser diode is considered deteriorated.
Are there any (HF)RF amplifiers that are tuned to 1.2V? And laser current amplifiers that are connected directly behind the laser. It's very complex You would probably have to calculate the laser current through the series resistance. U/R = I I still have a lot of unanswered questions, it's not that easy to understand everything. I won't twist the Polti APC automatic power control at first. I'm afraid that the laser will receive too much power and will soon become defective. You also have to remove the laser unit, I don't know how yet. I won't be turning the pot on the device anymore. There's probably no voltage test point for Focus Gain , Tracking Balance either?
You might find useful info here as this covered all the typical adjustments:
https://www.diyaudio.com/community/threads/sony-cdp790-and-kss240-restoration-project.226288/
The RF amps are not tuned to 1.2 volts, they simply amplifiy the photodiode arrays output which is determined purely by the level of laser energy reflected from the disc. 1.2 volt is the typical peak to peak level seen from a good representative commercial CD and a laser that has the correct optical output (as measured wiuth a laser power meter).
As you say, calculating the current from the voltage developed across the resistor is the only way to know the current. Optical output from a laser rises very rapidly as current increases, it is very non linear. Having said that the laser diode is typically run well below its maximum current rating and there is plenty of leeway, however the higher the current and the shorter the life will be (and the hotter it will run).
https://www.diyaudio.com/community/threads/sony-cdp790-and-kss240-restoration-project.226288/
The RF amps are not tuned to 1.2 volts, they simply amplifiy the photodiode arrays output which is determined purely by the level of laser energy reflected from the disc. 1.2 volt is the typical peak to peak level seen from a good representative commercial CD and a laser that has the correct optical output (as measured wiuth a laser power meter).
As you say, calculating the current from the voltage developed across the resistor is the only way to know the current. Optical output from a laser rises very rapidly as current increases, it is very non linear. Having said that the laser diode is typically run well below its maximum current rating and there is plenty of leeway, however the higher the current and the shorter the life will be (and the hotter it will run).
Thanks for the information. I don't know how much power the Laser gets with a laser current of 50mA, for example? CD lasers have 5mW max. Power according to the Data Sheet.How high is the laser power emitted at 50mA-60mA? I can't measure the voltage drop across the Series Resistance to determine the laser current. Everything is blocked up. But it would be interesting to know at 50-60mA laser current, what power is consumed by the Laser diode? Do you know ?
It doesn't really work like that as the diodes have a wide tolerance and vary one to another.
If you increase the current from zero you find the laser diode emits a dull red light but it is not 'lasing', it is just emitting light like an LED. Once the current reaches around 50ma lasing starts and the optical output starts to increase. From that point a very small increase in current causes a large increase in optical output. The problem is all the diodes are different.
If you look at the data sheet for a typical diode like the old Sharp LT022MC it has a threshold (when it starts lasing) from anywhere between 50 to 80 ma. So one pickup might start lasing at say 55ma and have a set current of 64ma to get the required output and another might begin lasing at 61ma and need 73ma to get the required output.
Once lasing a change in current of just a milliamp or two makes a big difference to the optical power emitted.
The laser diodes used in pickups are run well below their absolute maximum rating. The forward voltage (dropped across the diode) also varies a lot and can be as low as around 1.8 volts and as high as 2.2 volts. They all vary one to another. Power dissipated is around 140 milliwatts which might not sound much but it generates a lot of heat in a very tiny area (the laser diode chip itself).
If you increase the current from zero you find the laser diode emits a dull red light but it is not 'lasing', it is just emitting light like an LED. Once the current reaches around 50ma lasing starts and the optical output starts to increase. From that point a very small increase in current causes a large increase in optical output. The problem is all the diodes are different.
If you look at the data sheet for a typical diode like the old Sharp LT022MC it has a threshold (when it starts lasing) from anywhere between 50 to 80 ma. So one pickup might start lasing at say 55ma and have a set current of 64ma to get the required output and another might begin lasing at 61ma and need 73ma to get the required output.
Once lasing a change in current of just a milliamp or two makes a big difference to the optical power emitted.
The laser diodes used in pickups are run well below their absolute maximum rating. The forward voltage (dropped across the diode) also varies a lot and can be as low as around 1.8 volts and as high as 2.2 volts. They all vary one to another. Power dissipated is around 140 milliwatts which might not sound much but it generates a lot of heat in a very tiny area (the laser diode chip itself).
I agree - go to images in post #10+15 under
https://www.diyaudio.com/community/...v-dead-transport-section.410367/#post-7637179
This Sony servo board is mostly in use with laser unit KSS-272A - the BSL motor board "1-641-763" probably in some other additional models.
Leaked caps are here to observe very often (with all consequences).
Nevertheless I remain convinced that hardly any other laser unit has a shorter lifespan than the KSS series due the laser diode, the foil (flat) cable and the plastic suspension of the lens - go for some images to
https://vintage-audio-laser.com/A-l-atelier-page-69
The fact that reliable laser units like JVC Optima series or Sanyo's SF-91 are still available - even as NOS versions for reasonable costs (in opposite to the KSS-units for SONY ES and Accuphase) is proof of this for me.
Go also to
http://www.hifimuseum.de/sony-cdp-557-esd.html
http://www.hifimuseum.de/3256.html
for further information.
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