Electrical Adjustment of a laser pickup

[Salar]

Hello,
I´ll have to do some adjustment on my Nakamichi from ´86, which basically is a Sony.
Unluckily, I´ll 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:
I´ll 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

[anatech]

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.

[Salar]

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 CD´s 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 CD´s 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?

[anatech]

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

[Salar]

Hi chris!
Thanks a lot for the exact description! I am collecting CD´s 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

[anatech]

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

[Salar]

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

[anatech]

Hi Salar,

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

[Salar]

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

[anatech]

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