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KSS-272A Substitution of laser diode
KSS-272A Substitution of laser diode
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Old 4th July 2020, 01:09 PM   #11
ManoloMos is offline ManoloMos  Spain
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Join Date: Dec 2019
Location: Canary Islands
Quote:
Originally Posted by vt4c View Post
ManoloMos,
Thank you for sharing your excellent work. I own a CDP with KSS-151A pick-up and are looking forward to your experiment again on changing the laser diode.
Hello. I've bought some ffc/fpc 20 pin 1,25 pitch cables and connectors for the KSS-151A, I'll try to change the diode laser in an KSS-151A and I'll tell in this forum.
For the KSS-151A we have to do a little circuit, to polarizase each a-b-c-d-e-f diode separately. I have to do this circuit because in almost all CD's player with KSS-151A or KSS-190A, the A C and B D diodes are joined, we need to see these diodes serparately.
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Old 4th July 2020, 01:20 PM   #12
ManoloMos is offline ManoloMos  Spain
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Join Date: Dec 2019
Location: Canary Islands
Quote:
Originally Posted by Salar View Post
Tried to contact Ken Klements for my laser diode swap project.
There are some photos floating arond by laser repairers
What struck me was the fact that one can see the beam spots
superimposed over the photodiode-array spots.
Maybe this effect can be used for aligning?
See photos below:
Hello. No, in fact, I doubt that in reality, the laser impact in the photodiode array be like in this picture.
If you see, almost all laser pickups has a part when you can see the A-B-C-D-E-F diodes. This makes me think that the method used in factory for to adjst the laser diodes is with a machine reading the A...F diodes. To adjust it, you have to put a mirror front the pickup, and to excite the focus coil with low frequency signal and a bit of dc voltage.

When you are triying to adjust the laser, you see that the first diodes to reach signal are E and F, then the others. Find E-F is easy, to calibrate A-B-C-D diodes is the most difficult. So, when you are triying to find the best position, you make a mental representation of how the laser are lighning the photodiodes. So, that makes me think that this pictures is a artistic representation, I don't think it be true in reality. E-F.

I hope another technician or engineers trying to do the same like I, so with more experiences, we can reach more knowledge in this issue.

In the manual service of the Pioneer P-D70 appears how to adjust the laser pickup, with an oscilloscope and a external device, this manual is the key.
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Old 4th July 2020, 02:07 PM   #13
ManoloMos is offline ManoloMos  Spain
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Join Date: Dec 2019
Location: Canary Islands
Quote:
Originally Posted by percival007 View Post
It would have been interesting if you had reassembled the Laser Block at this point, I suspect it may have worked.

In my experience repairing CD Players, very few emitting Diodes have failed, it is usually the Receiving Diode array or more likely dust where it's ''not usually'' accessible.
You have proved that it is accessible and a good clean 'probably' cured your problem.

I slute your perseverence !!

Hello. The second KSS-272a, belongs to a CD i bought 8 or more years. It used to skip some tracks in some cds. The solution was to adjust the position of the part who contains the movil lens. This part has two screws underneath which are very difficult to adjust while the cd is playing. But adjust wasn't this screws, the screws are above, and the best performance was moving this piece to a side. This made me think that:

1 The laser pickup was bad ajusted in factory.
2 The plastic pieces were deformed, a tiny deformation, but enought for to worse the performance.

So, repair this kind of lasers is nos only to changle the laser, is necesary to adjusto, to clean and to solve any problem that could appear.

It's not easy.

The laser was replaced because the signal was a bit noise. Though the power laser was good, it seemed a bit noise and I wanted to experimentize.

When the laser gets older, it seems that besides to get weaker, the signal is noisy in the oscilloscope. I don't know why it happens.
One of the main property of the laser, is the phase cleanliness. I think maybe it appears phase noise, and without phase cleanliness, the performance get poor.
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Old 8th July 2020, 07:22 PM   #14
Salar is offline Salar  Germany
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Join Date: Feb 2006
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Quote:
When the laser gets older, it seems that besides to get weaker, the signal is noisy in the oscilloscope. I don't know why it happens.
One of the main property of the laser, is the phase cleanliness. I think maybe it appears phase noise, and without phase cleanliness, the performance get poor.
That is very Interesting and might explain, why the signals of my BU-1 transports are a bit noisy.

Quote:
When you are triying to adjust the laser, you see that the first diodes to reach signal are E and F, then the others. Find E-F is easy, to calibrate A-B-C-D diodes is the most difficult. So, when you are triying to find the best position, you make a mental representation of how the laser are lighning the photodiodes. So, that makes me think that this pictures is a artistic representation, I don't think it be true in reality. E-F.
At which point does the grating come into play? As far as I understand, the grating does not influence the position of the side beams but their brightness...?
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Old 9th July 2020, 04:17 PM   #15
ManoloMos is offline ManoloMos  Spain
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Join Date: Dec 2019
Location: Canary Islands
Hello. I assume that the grating is adjusted in factory and it is not necessary to adjust its position. In one KSS-121A that I've talked here before, the grating unsticked and I didn't know its original position, well, at third try it worked again. The position is such that the piece holes or marks coincide with the vertical or horizontal plane of the metal piece which contain the grating. The grating is not a real problem.

Why the signal is noisy?

Laser diode weak.
Laser diode aged?
Dust, tobacco ash.
Lens with moss, fungus, or other kind of degradation of th anti reflecting coate.
Some tecnician oiled the pickup, and the oil reach the lens. In the KSS-271a that now I'm trying to repair happened it.
Mechanical disajustment of theh azimuth or other adjust due to the platic deformation, ageing, etc...
And I've found in one BU-1C a big problem. The first BU-1C that I repair, the signal was right, but the power output at the lens was 750uw. The normal output is 210-250uW. The problem was that the lens, that you can see in the pictures, is made of two pieces or two lens sticked with glue. Well, the glue is degraded and it have losed its transparency.

BU-1C Disease - Google Photos
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Old 9th July 2020, 05:29 PM   #16
Salar is offline Salar  Germany
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Join Date: Feb 2006
Location: Germany
Quote:
The position is such that the piece holes or marks coincide with the vertical or horizontal plane of the metal piece which contain the grating.
Here is a link to photos of a BU-1 I opened:
Dead Laser Pickups - why not replacing the Diode only?

In case the link does not connect to the post directly, it is post #31
So the left and right notches of the plastic housing should align
to the recess in the tube I assume?
Unfortunately I did sent this BU-1 photographed to a DIYaudio member
who wanted to figure out a diode swap - I gave him not only this BU-1 but also 8 or 10 LT022MC diodes and I did buy him a working CDP-102 with BU-1 as reference.
This was in December 2018 and no progress at all. I asked him to ship everything back several times one week ago but until now he did not reply. Hope to get the stuff back to try the swap myself. I am also very eager to check if the APCcan be modified to implement modern diodes. Again, great work!
 

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