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An Idea for saving Laser Life - amplifying the current?
An Idea for saving Laser Life - amplifying the current?
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Old 16th November 2018, 09:35 AM   #61
Salar is offline Salar  Germany
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Perfect, thanks! I will try this today and monitor the E-F Output before and after the mod using a disc with simulated errors
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Old 16th November 2018, 09:59 AM   #62
Mooly is offline Mooly  United Kingdom
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An Idea for saving Laser Life - amplifying the current?
Remember that the final error waveforms should always be close to zero.

When the light reaching the two diodes is equal, the error signal is minimal... its centred on track. If you increase the gain of the amp stages, the final error signal still has to be the same minimal value.

So don't expect to see the final error signal increase, the gain change will just give the servo enough range to work with to initially get the beam on track. Increasing the gain to much will increase the noise on the error signal while still keeping the fundamental waveform the same.
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Old 16th November 2018, 11:36 AM   #63
Salar is offline Salar  Germany
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This is the tracking error signal caused by dropout, Shouldn`t I see
peaks higher in amplitude symmetrical to the fundamental signal after the mod...?
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File Type: jpg IMG_5005.jpg (346.2 KB, 20 views)
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Old 16th November 2018, 02:35 PM   #64
Mooly is offline Mooly  United Kingdom
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An Idea for saving Laser Life - amplifying the current?
I'm not so sure you would tbh. That signal is what ultimately drives the tracking coils of the pickup. If that signal were bigger, the lens would move further. If its correct now then it should also be similar after the mod.

The defect on the disc is fixed and so the waveform needed to correct that defect is 'fixed'. Its like a servo system on an amp for DC offset. The error voltage is the same no matter what the internal gain structure of the servo... within limits until the servo loses lock and goes out of range.

You will have to try that and see what happens in practice.
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Old Today, 12:18 AM   #65
Salar is offline Salar  Germany
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And I tried...

First of all, please ignore the photographs and schematics posted
before, there are some errors. What follows is correct.


One wrong assumption is the amplitude of the eyepattern. It is 1.2V overall but only 1Vp-p. The schematic from Luxman forgot
the decimal point btw, 12V will definately shorten the laser diodeīs
life to less than a picosecond

The second error was R105. I calculated a wrong value by not considering VR101. Many thanks to Mooly for correcting that.

I raised the value of the resistors in the schematics by 1.5.
This resulted in 1.2Vp-p in the eyepattern and the opportunity to lower the level to 1Vp-p as stated in the service manuals.

I made this modification on two BU-1C equipped players today, a Sony CDP-103 and a Sony CDP-302. On both I could lower laser power.
To my very surprise, lowering the power by 0.2V meant just a tiny almost unperceptible counterclockwise turn of VR1,
a 10k trimmer on the BU-1C laser board.
I really wonder how they aligned during production, its like microsurgery.
This could be due to aging, but VR101 for E-F balance has to be reajusted as well, which was easy with a sensible margin.
Best to do so is by pressing the search button and to watch the E-F error "peaks". Turn the trimpot until they are symmetrical.
But both players also worked without readjustung E-F balance.

I asked Sam from "Sams Laser FAQ" if the mod was sensible.
His answer was:
There should be no harm in
increasing the PD amplifier gain. At worst it will add noise and make
things worse, but should not damage anything. Don't increase it beyond
the spec'd value.
(Which we do not know)
Running just at threshold will not be reliable but I have not heard of
any real risks unless the power regulation feedback becomes unstable.

In general, the laser diode power should be quite constant until
near end-of-life since it's feedback regulated. Only when the diode
cannot output sufficient power at the diode current limit will
regulation fail and the power will decline. Nothing much can be
done on the LD side for that


So running the laser with lesser power will not do any harm?

Not that I'm aware of, at least not in terms of the LD chip itself.
However, as I said, if the regulation becomes unstable, that could
damage it. I do not know if that can happen.


But it is not proven that itīs life can be prolonged as it runs producing lesser heat…?

Well, yes, lower current = lower heat = longer life. But it's not an exact
science.
If the LD regulation circuit isn't maxed out, the diode should be OK since it's
using the actual output of the LD inside the can. That's the test.

Now, in principle, the monitor photodiode response can change. I don't know
if it does though in any significant way over time.


Well, as the slightest turn of the trimmer for laser power resulted in
relatively drastic changes in amplitude. I assume the regulation circuit must have a headroom...
In other words I cannot imagine a circuit that can be maxed out by turning the trimmer just a bit.
But as a result I will put multiturn trimmers in the BU-C for adjusting laser power.

I am not sure whether not changing R109 and R110 (in contrast to an earlier
schmatic) is correct. But I think R108 does the job already.

So if everything is correct now, we could start a new thread and do a database of players using the CX2019, with the feedback resistors original and altered values.
I.e. the CX20109 feedback resistorīs values in a Nakamichi OMS7II/OMS5II CD player (using a KSS-123A laser) are different from a BU-1C.

All the best,
Salar
Attached Images
File Type: jpg BU-1C-Schematic_Altered_Values_FINAL.jpg (786.4 KB, 3 views)
File Type: jpg Eyepattern_18K_before.jpg (800.8 KB, 3 views)
File Type: jpg Eyepattern-27k.jpg (937.3 KB, 3 views)
File Type: jpg E-F-Balance.jpg (624.8 KB, 3 views)

Last edited by Salar; Today at 12:35 AM.
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Old Today, 07:46 AM   #66
Mooly is offline Mooly  United Kingdom
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An Idea for saving Laser Life - amplifying the current?
Thats all great work and very comprehensive. I would agree with the comment on the LD maintaining its output until the very end, that's exactly how the OPC (optical power control) circuit is designed to work.

The current flowing in the laser diode vs lasing action is extremely non linear and that is why you see a relatively big jump in RF for a little change in LD current.
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