Electrical Adjustment of a laser pickup - diyAudio
Go Back   Home > Forums > Source & Line > Digital Source

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 24th October 2006, 10:57 AM   #1
Salar is offline Salar  Germany
diyAudio Member
 
Join Date: Feb 2006
Location: Germany
Default Electrical Adjustment of a laser pickup

Hello,
IŽll have to do some adjustment on my Nakamichi from Ž86, which basically is a Sony.
Unluckily, IŽll also have to make an adjustment, which is seldomly required.
You can find the description of the adjustment in the file attached.
(It was not very well translated I guess.)
What troubles me is step 5 of the adjustment procedure:
IŽll need asignal generator, but could use my other CD-Player, playing the test tone needed. (it has to be fed to an IC for adjustment)
The maximum level is 2.5 V at 50 kiloohms, Load impedance over 1 Kiloohm, how do I get 300mV at 220kilohms from that? Could anybody do the math for me?
Also, a bandpassfilter is needed for adjustment. I could loop the signal through my mixing console and apply a filter there before monitoring the resulting signal on the scope (I guess also a peakmeter is needed, but is not mentioned in the service manual.)
Maybe, somebody knows, how steep/flat this band pass filter should be?
All the best,
Salar
Attached Files
File Type: pdf oms5eii_#3.pdf (85.6 KB, 272 views)
  Reply With Quote
Old 26th October 2006, 08:54 PM   #2
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi Salar,
Adjust the gain while the unit is playing a CD normally. The sweet spot is just after the low frequency content settles down and before the high frequency noise gets larger. Standard Sony method, works well for me.

One problem I've noticed with those heads is that the pole piece gets sticky with the lens assembly. Watch for sticky heads. You can't clean them either.

I also PM'd you the same response, but posted for the benefit of other members.

-Chris

Edit: The transport is from NEC.
  Reply With Quote
Old 27th October 2006, 07:39 AM   #3
Salar is offline Salar  Germany
diyAudio Member
 
Join Date: Feb 2006
Location: Germany
Hi Chris!
Thanks for the quick reply - so a frequency generator is not needed?
What about a test CD - is the Test - CD from Philips you mentioned in the KSS-151 thread available somewhere? (Looks like the YEDS-18 CDŽs from Sony are sold out)
Do you have the name/part number of the Test-CD?
But I can imagine, that a well manufactured Audio CD will help as well, especially CDŽs from the beginning of that era, from which I assume, that specifications were very tight...
All the best,
Salar

BTW, my english is not perfect, what is a pole piece?
  Reply With Quote
Old 27th October 2006, 12:55 PM   #4
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi Salar,
For gain adjustments it's critical that the exact test disc specified be used. Since you are not following the service manual, pick out a good defect free CD. Monitor the RF (or EYE pattern) and use the disc with a large, clear and stable RF pattern. This will minimize servo noise.

Tracking gains are not precise really. What you do is monitor the tracking error or output terminal. Note where the the controls are before you start. Turn the gain down slightly until the wave starts showing a low frequency component. Then turn it up until the low frequency component is greatly reduced and high frequency noise starts to show up. Back the control off in between these two points. You can increase or decrease the gain from this point a little. Car decks tend more to a little high frequency noise (helps track with bumps). A home machine may want the gain a little lower (doesn't over react to defects on the disc).

Now you know my tuning secrets.

On a KSS-123A, the lens and coils ride up and down around a central pole. There is a bearing in the lens assembly. Anything in there will gum things up. I've tried everything with no luck once these get sticky. Often that is what causes head replacement on these.

Salar, your English is just fine from my end.

-Chris
  Reply With Quote
Old 27th October 2006, 08:43 PM   #5
Salar is offline Salar  Germany
diyAudio Member
 
Join Date: Feb 2006
Location: Germany
Hi chris!
Thanks a lot for the exact description! I am collecting CDŽs for about 20 years, so I guess, one perfectly manufactured can be found. I hope, the assemby will not gum up when being stored. I guess I will need the next replacement at least seven yeras ahead. The units I bought were spare parts for AKAI, btw.
All the best,
Salar
  Reply With Quote
Old 28th October 2006, 02:19 AM   #6
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi Salar,
I bought some Akai stock too! I was lucky, but it was after the fact.

Just pick the best CD's. I have some new and some old that are quite good. Your stored heads should be okay as they are sealed. (I hope, because I have a couple still for my OMS-4)

-Chris
  Reply With Quote
Old 28th October 2006, 10:03 AM   #7
Salar is offline Salar  Germany
diyAudio Member
 
Join Date: Feb 2006
Location: Germany
Hi Chris!
Which fact do you mean? Did Sony fix the "pole problem" in later stocks? Maybe, the KSS-123A should be stored with the lens facing upward?
I will make the readjustment when I get some good electrolytic capacitors for the D/A board - maybe you noticed that I redesigned the cabinet, but now it has become more complicated to open the player, so i want to do everything on one occasion. I replaced the original Nichicons for some 105Grade(Celsius) types, but the Nak now lacks a little bit of bass and the treble does not sound clear anymore. Unfortunately, Panasonic FC / Nichicons / OsCons are not easy to get here in Berlin, but somebody here sells Blackgates - for about 35U$ each ... argh
All the best,
Salar
  Reply With Quote
Old 28th October 2006, 02:42 PM   #8
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi Salar,
Quote:
I was lucky, but it was after the fact.
After I used a lot. I did sell a few and kept a couple for my own machine.
I don't think it matters which way they are stored. On the side might be best.

I've found the 105 ° caps are not as good electrically as the 85 ° caps. Bypass big ones with 1 uF box films. Anything that is 4u7 and below can be replaced by Wima film types (thanks again MikeB!). I suspect a bypassed 85 ° might be as good as a blackgate, just a guess.

-Chris
  Reply With Quote
Old 4th November 2006, 07:06 PM   #9
Salar is offline Salar  Germany
diyAudio Member
 
Join Date: Feb 2006
Location: Germany
Hi Chris,
finished the electronical adjustment today (5.00 am)
Well, unluckily I could not adjust the tracking gain with a scope - the pins of the scope did kind of shorten the amp for the tracking circuit - even with using a resistor of one megaohms.
But what seemed to help was monitoring the time the laser takes, when it has to jump from the first to the last track and vice versa. Nak sometimes almost semed to fail when doing so.

After some time of "just travelling" the motors/servos switches to some kind of audible search mode for some moments, (one hears them "cirping") until the beginning of the track is found and the motors run silent again.
I adjusted the tracking gain in a way that this moment does take as less time as possible and sounds "precise"
Putting the gain high results in a hissing noise, I guess? (Lenscoils?)
This was the way it was before. Now the Nak is still not fast (about 5-6 seconds from the first to the last track, lets say 50 minutes of disc time to travel), but was maybe a second faster, when I bought it.
Again, thanks for your help,
All the best,
Salar
  Reply With Quote
Old 5th November 2006, 02:49 AM   #10
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi Salar,
The hiss sound is the lens assembly. The oscilloscope should not load the servos in any way. You have an audio band signal driven with a class "B" output stage. Your 'scope probe will be 10 Meg shunted by a small capacitance. A trival load. Look for FO and TO test points.

-Chris
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Please look that Laser Pickup... Zeljko Digital Source 12 29th July 2012 11:48 AM
Laser pickup adjustment on Accuphase CD player Lulu_the_cat Digital Source 1 24th January 2010 01:54 PM
need help with CDM4 laser adjustment vubkevin Digital Source 2 23rd August 2009 10:26 PM
Can anyone help me identify this laser pickup? mr_push_pull Parts 3 14th December 2006 10:35 PM
NAD 510 Laser pickup squirrel69 Digital Source 1 7th April 2006 09:41 PM


New To Site? Need Help?

All times are GMT. The time now is 11:25 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2