Nakamichi OMS-5EII - Track offset is drifting! - diyAudio
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Old 16th July 2007, 12:10 AM   #1
Salar is offline Salar  Germany
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Join Date: Feb 2006
Location: Germany
Default Nakamichi OMS-5EII - Track offset is drifting!

Hello,
today, I tried to realign my Nak, using a scope.
I did replace some parts last year, disc motor and laser as well as the belts, and I did also replace all electrolytic capacitors.
But after one year the symptoms are now:
After powering up, the nak needs at least half an hour of warming up to work properly.
In the beginning it will not find the first track or play a burned CD without a crackling noise. (The same sound when you play a "faded" CD, where the dye has bleached)After this long time of warming up, the Nak plays CDs well, but still needs a long time to find a track. (lets say about 5-7seconds)
Sometimes the Nak will find and play a track within a second, but this effect is not repeatable nor disk-dependend. (Even with the Sony test-CD YEDS-18, which claims to have almost no manufacturing errors wobble or jitter, the Nak needs time to find a track when searching for it)

When the Nak tries to catch a track, I can hear strong clicking noises, of "try and error". Also the rotation speed seems to vary a lot during this process.
But after the track is found, playback works fine, I can not hear audible errors.

When adjust tracking/focus offset today, I noticed on my scope that DC level shifts after some minutes, mostly to a higher gain. Not much, but enough to have to adjust the variable resistors again.

Generally I tried two approaches when adjusting the Nak, using the description in the service manual or simply adjusting while only observing the eyepattern.
But with both approaches, the "find track" problem remains.
Any ideas? What about the transistors? They are now 20 years of age, should I try to replace them? As I said before, laser unit, belts,motors, electrolytic capacitors were replaced last year... i think I did not spoil something last year, because the problem was already there before the replacements, but it was not as strong as today...
Thanx in advance for your help!!!
All the best, Salar
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Old 3rd August 2007, 12:57 PM   #2
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Join Date: Jul 2006
Try measuring the voltage over the track motor using an analogue meter. See if the voltage builds up while it is running. if so then there is a "blind spot" on it and must be replaced.
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