Diffraction Grating - Dear Sony Engineers, how did You do your Miracles?

Salar

Member
2006-02-08 8:40 pm
Germany
I want to know how the diffraction grating in three beam lasers was aligned in in the factory. Threadlocker indicates it had to.
In Sony lasers from the mid-eighties to early nineties, access to the grating is very limited. A hole on the side, that´s all.

But the grating, shaped like a coin, was to align not only in horizontal axis but also in rotation.
Also there is a spring between the laser and grating which puts some pressure on it.
Removing the laserdiode and putting it on again seems destroy the alignment (at least to my observance - but in my only attempt yet the grating became loose because there was was not enough threadlocker applied)

So any first hand observances are very welcome. Please no assumptions or guesses. Maybe somebody knows (probably retired) employees of Sony to explain the process and the rigs needed?

BTW, as far as I know, in Pioneer players it was possible to readjust the grating during servicing. But not for many models.

All the best,
Salar
 

Salar

Member
2006-02-08 8:40 pm
Germany
Forgot to mention:
It needs adjustment - when the laser diode has to replaced.
Replacing the diode was never
intended being part of the Sony servicing process.
As far as I know, swapping the diode was not successfully done yet,
but more a matter of trial and error.


Spares, especially for first generation players, are gone.
Best case - you might find an original diode.
Still you would probably need alignment.

Worst case - you´ll have to use a type thats an actual one. Different astigmatism, different power ratings and pinout.

BTW this thread should not be about:
"You can buy a working one from ebay and scavenge it"
"Diodes don´t die that fast, my player is 30 years old"
"It might be the motor as well"
"Did you clean / grease it"
"Nowadays people download their music"
"I prefer Hi-Res anyway"

Just: Old three beam laser - replacing the diode. How to adjust the grating?

In this community or in the outer rims there might be some people to explain the process?
いつか会えるといいですね,
Salar
 
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I don't know if it is similar to yamaha laser pick-up mlp-7 (3 beam) but there are some instructions in service manual of yamaha cdx-1100,2000,5000. Two channel oscilloscope is needed. One channel to EFMI (RF), second to TER terminal (pin 8 of IC102, which is output of EFB op-amp). The amplitude needs to be min 150mVp-p.
Adjustement is made with little screw in the pick-up assembly. Hope it helps.
 
Can I suggest you have a read of a Pioneer Service Manual.
Try this one............
Pioneer PD-91 Manual - Compact Disc Player - HiFi Engine

Have a read through the Grating alignment for that one, it may give you some pointers.
It was always a joy to align a Pioneer from this era, you could get 'em to play anything round and shiny !!

I think it's probably similar to the Yamaha mentioned above but the more info the better(?).

James.
 
Absolutely!
But the challenge will be to "translate" the grating adjustment to other
players like Sony. (Besides rotating a grating that was never designed for being
aligned during servicing)

Ken Clements also described the process in his book
"Understanding and Servicing CD Players"

The search terms "Clements grating adjustment" will show excerpts in google books.
 
On the Pioneers I got it down to be able to do it from just the Tracking Error Waveform.

In Test Mode with just the Focus Servo working, one was able to gently run the Grating alignment to one end, then, slowly, turn the adjustment to the the other end of its travel, counting the Peaks of the Tracking Error waveform.
I seem to remember there being about 9 or 12 ((?) it's about 15 years since I last did one!) so counting 4 (or 6) back the other way, align the TE for maximum output. Turn the TE on and the Player used to play, or if not, one more turn of the Grating to the next Peak, aligned for max O/P, would be the right one.
I used to use the Technics Test CD to make sure all was well (0.8mm scratch or spot(?)) and then I used to have my own CD which I had scratched myself. If it could play this I had it sorted. I could get any Pioneer to play it, Sony's with a KSS-240 would also be able to but not so many others especially after the introduction of 'Automatic Set-Up' within the Chip Sets.

We had a tool supplied by Pioneer but I made my own, filing down a 'minus' screw-driver untill it just fitted perfectly.
You may have to do something similar.

I believe Sony Laserdisc Players used to have to have the Grating adjusted, maybe worth a look in a Service Manual for one of those for some more pointers.

James.
 

Salar

Member
2006-02-08 8:40 pm
Germany
Is the Tracking error Signal the same as the (combined?) E-F Signal?
And how turn a screw on a moving laser?
O.k, the gear will brake the laser but there might be some play.
And with a gearless linear drive, it might become worse because it can be moved without friction...:confused:
 
Yes, the E-F outputs from the Laser are combined to give the Tracking Error (TE) Signal.

On the Pioneers, in Test Mode with the TE Servo turned Off there was no drive to the Sled so the Grating could be adjusted with ease.
What Model is it you're working on? Is there any Test Mode accessible?
 
Where are you getting the new Diodes from?
Can you get both the emitting and receiving Diodes? I often find a failed Laser still outputs correctly but the information coming from it is low so in these instances I assume it is the Receiving Diode.
Will you be replacing these also?
 
Never heard that receiving diodes (photodiodes) age, but
I might be wrong. I will try actual laser diodes from Rohm
They consume lesser power and emit more light so I hope that modding
the apc will be easy. Biggest obstacles:
The probably different astigmatism/spread of the beams
A mechanical adaptor has to be build to fit the 5.6 mm
cans of modern diodes
Probably some gauge has to be milled to help
adjust the grating precisely
The controller of the player has to be defeated to make
the laser emit even when reading fails.
Maybe even some some kind of polycarbonate "adjustment disc"
has to be made: No pits and lands but an equally reflecting
layer for rough adjustment, a normal disc for finer adjustment.
Nevertheless I will start with some "original" sharp diodes
bought from ebay, to have an equal replacement and
develop a method. The Bu-1c uses Sharp.
Would be a pity not to save those old great machines!
 
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Never heard that receiving diodes (photodiodes) age............

Quite often I find the Emitting Diode to be still working OK at a Power within Specification so I have always assumed it was the Receiving Diode which was failing and not outputting the required pk-pk value of RF Information.

Would be a pity not to save those old great machines!

I agree. I fortunately have built up a stock of spare Lasers for my own Pioneer. The original is no longer available from anywhere.

Good Luck and do keep us informed of your progress.