Nakamichi OMS-5EII/7EII weak error correction - 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 9th December 2007, 05:06 PM   #1
Salar is offline Salar  Germany
diyAudio Member
 
Join Date: Feb 2006
Location: Germany
Default Nakamichi OMS-5EII/7EII weak error correction

Hi,
my Nak already clicks with errors of about 0.375 mm.
Another gear of mine, a Sony CDP-X5000 plays fine with errors of about 1.125mm (Got this measurements with Digital recording´s "CD-Check".)
I swapped the laser two years ago , made any adjustment possible according to the service manual. (I am again playing around with the trimmers in the moment)
I also swapped all caps in the electronics, with no improvement.
I even swapped the discmotor to the same model but with a longer shaft, so I took the occasion to build an aluminium spacer with an additional bearing to keep vibrations from the disc motor low. The bearing works perfect, but has no influence on the Nak´s poor error correction.
And no, the pole piece of the laser is not sticky.
Listening to both units through my Parasound DAC, I have the impression that the Nak sounds more grainy, maybe because of small interpolated readout errors.
I still have spare parts, for example two laser heads to give the Nak a long life, so is there anything I could improve electronically in the servo circuit? (i.e swapping opamps)
All the best, Salar
  Reply With Quote
Old 10th December 2007, 01:16 AM   #2
Nanook is offline Nanook  Canada
diyAudio Member
 
Nanook's Avatar
 
Join Date: Feb 2004
Location: Chinook Country.Alberta
Default not a tech but....

try to find the diode bias for the laser and adjust it . I don't have a manual , but perhaps some of the techie types might.
__________________
stew -"A sane man in an insane world appears insane."
  Reply With Quote
Old 10th December 2007, 12:08 PM   #3
Salar is offline Salar  Germany
diyAudio Member
 
Join Date: Feb 2006
Location: Germany
Hi Nanook,
thanks for the reply, but the laser is only two years old.
I also HAVE the service manual.
Trimming the laser diode bias is the last thing one should do.
If you´ll have to, the laser will probably fail anyway in the near future.
Some tech once stated to me, that lasers are more durable than expected. If they are not working correct, it is very often not the dirty lens but the dirty mirror which splits the beam.
No, I guess, the problem lies somewhere in the servo circuit - because the range of trimming, until you hear an audible effect, is v e r y wide, almost 3/4 of a turn on any trimpot.
The eyepattern on my scope is always a bit noisy. The diamond shapes are relatively clear, but the the upper/lower edges of the eyepattern are noisy.
Trimming the focus offset will have the most visible effect on the eyepattern.
The amplitude rises - this is okay-, but if you go too far, it will become too noisy. I guess, this is also normal.
But trimming E-F balance has no visible effect on the eyepattern.
Trimming E-F according to the service manual (You have to observe the E-F signal in service mode,) always delivers a very noisy E-F, which bounces in it´s peaks and amplitude duration. This is very hard to observe for right adjustment. If you trim off too far, the disc motor will suddenly speed up to maybe ten times ore more. Don´t know, wether this is normal.
My workaround is to use a CD with two very long tracks and simply adjust E-F while skipping between the tracks.
But cklicking with errors of only 0.3 mm does not seem normal to me.
For E-F, I now use a CD which has three very definable but small errors/scratches (Keith Jarrett, "Tokyo Concert" from the "Sun Bear Concerts" btw.).
I sometimes get the E-F right, and there are no audible clicks - and i really try to trim in fractions of a millimeter - and the next day, the CD will click again...
I still have the issue of a german magazine called "Audio" from May 1987, where the Revox B226, Denon DCD-3300, Marantz CD-94, Kenwood DP-3300, Meridian 207 and Nakamichi OMS-5/7EII were reviewed - all of them state of the art in their times. All players, using less Philips and Sony electronics, at least the Denon and Nak sharing the same laser (KSS-123A) , got all the best possible notes for error correction...
I will swap the laser today, maybe I simply swapped a weak original laser to a mechanically misaligned replacement...
But when I designed the spacer and additional bearing for the disc motor, with the help of a mechanic who specialized himself in repairing bearings of turntables, we found out, that the mechanics have more tolerances than expected. (i.e. the housing of the disc-motor has tolerances, also the angle and thickness of the shaft, and therefor the disc tabe might be slightly off).
So I still guess, something in the servo circuit has become weak...
All the best, Salar
  Reply With Quote
Old 16th December 2007, 12:34 PM   #4
Salar is offline Salar  Germany
diyAudio Member
 
Join Date: Feb 2006
Location: Germany
O.K.,
I found the sweet spot.I am in a hurry in the moment, so I will post details later.
BUT:
The player will only correct/play heavy scratches one to two hours after being powered up !!!!!! The service manual states, the electronics should settle within three minutes
Any ideas about that? Maybe a defective transistor?
All the best, Salar
  Reply With Quote
Old 16th December 2007, 05:25 PM   #5
diyAudio Member
 
QSerraTico_Tico's Avatar
 
Join Date: Oct 2004
Quote:
Originally posted by Salar
O.K.,
I found the sweet spot.I am in a hurry in the moment, so I will post details later.
BUT:
The player will only correct/play heavy scratches one to two hours after being powered up !!!!!! The service manual states, the electronics should settle within three minutes
Any ideas about that? Maybe a defective transistor?
All the best, Salar
Adjust focus gain for optimum results with black stripe, 1 mm wide, on a CD.
  Reply With Quote
Old 17th December 2007, 01:43 AM   #6
Salar is offline Salar  Germany
diyAudio Member
 
Join Date: Feb 2006
Location: Germany
Hi Tico,
I have such a CD, but on my old scope, dropout and recovery are not easy to judge.
You can read further details here:
http://www.diyaudio.com/forums/showt...26#post1376726
All the best,
Salar
  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
Providing Digital Out to a Nakamichi OMS-5EII Salar Digital Source 15 11th July 2013 04:59 PM
Nakamichi OMS-5EII - Track offset is drifting! Salar Digital Source 1 3rd August 2007 01:57 PM
Nakamichi OMS-7EII ManUtd Digital Source 2 23rd October 2003 03:46 PM
Nakamichi OMS-7EII ManUtd Digital Source 0 21st October 2003 02:47 PM


New To Site? Need Help?

All times are GMT. The time now is 10:05 AM.


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