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Old 29th July 2008, 11:15 AM   #11
Mooly is offline Mooly  United Kingdom
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You need the ground that the RF amp uses ( as close to the rf amp ic as possible ) and to measure the RF as close as possible to the output of that amplifier. This does make a huge difference to how clean the signal appears in a lot of cases. Focus bias will affect the clarity of the eye pattern. If you connect probe tip and ground lead together on the scope and then touch both these to the chassis does the trace on the scope thicken due to noise ? If it does try a 10 ohm in the ground lead to the scope probe.
EF balance. Going from memory now, but try AC coupling the scope, and doing track searches while looking at the EF error waveform. As you keep doing this switch the scope back and forth between AC and DC coupling and try and get it so there is no shift as you do this. Long time is I have done one, but it should be fairly clear where the correct setting is.

Edit, ground = pin 7 of RF amp and use the designated EFM testpoint. The CX20108/9 chipset is nearly first generation and is the same as the original Sony D50 Discman (The first ever).
Dont think you are going to get this much better.
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Old 29th July 2008, 01:05 PM   #12
Salar is offline Salar  Germany
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Hi Mooly!
Thanks again!
So E-F should look like in the attachment of this post?
Never tried to measure close to the RF- amp, I am curious to do so, but it will take some weeks until I have the time to do it.
When I measured E-F balance , i first short circuited probe to ground (DC coupled) centered the flat line as reference on thze scope and then started measuring.

The D-50 is also part of my small collection of early players, never knew they had the same chipset, as well as the CDP-502ES/552ESD. I bought the service manual of the 552, because the setup in the Nak SM is described very badly. But even though the OMS and 552 have CX20108 and CX23035 in common, the setup routines are completely different...
Did you ever try tracking/servo gain and D.O.D in the nak?
All the best,
Sal
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Old 29th July 2008, 01:31 PM   #13
Salar is offline Salar  Germany
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Added the adjustment procedure...
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Old 29th July 2008, 05:25 PM   #14
Mooly is offline Mooly  United Kingdom
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That looks fine. As you turn the pot you will see the waveform shift and become non symetrical. It shows up more if I remember in track search. Oh by the way, Iv'e never worked on a Nak CPD. Worked on loads of Sonys, the D50 used the CX20108 etc. We used to sell a Fidelity player that was based on this chipset and these were always failing (the 20108). Changed probably around 6 to 8 altogether, never once on any other make of player. Must have been some PSU problem or spike seeing them off.
As for the other adjustments, as I say I don't think you will improve it a lot. For tracking gain connect scope to the tracking error waveform testpoint and as you turn up the gain a low frequency component will begin to appear in the waveform -- try it -- you want to back off slightly from this point so the fundamental just dissappears. Thats about it really
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Old 29th July 2008, 10:45 PM   #15
Salar is offline Salar  Germany
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Hi Mooly,
so. many coincidences! Well, the 20108 works for 19 years now, another could be used from a defective Nak (PSU) in if something should ever happen. I have a Fidelity B1 from that area, which I fixed after a transistor blew, but never got the quiminiscient current right. It will make way for a Shanling amp end of Summer.

So I should try to adjust tracking gain with a defective disc (like CD-Check) and watch for the low frequency component caused by the dropout?

BTW,could decoupling the M5218A give a small benefit? Decoupling was not used in the Nak at all, except some ferrite beads for the CX20108 and CX23035...
Thanks again,
Salar
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Old 30th July 2008, 07:00 AM   #16
Mooly is offline Mooly  United Kingdom
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Hi,
Use any good disc. As the tracking gain is increased the tracking error waveform will slowly start to oscillate up and down at a very low frequency. Adjust the tracking gain nearly up to this point, but so this fundamental is absent. The low frequency component isn't caused by drop out, it's to do with the stability of the whole tracking servo loop ( nyquist again )
Why not try starting another thread seeing if there are any NAK owners on the forum and ask how good there machines are. I really and trully think this is as good as it get's on this. Technology, in particular the software used in servo's etc has improved dramatically, as have the actual optical units themselves.
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Old 8th January 2010, 11:24 PM   #17
Salar is offline Salar  Germany
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Instead of starting a new thread, I dig this out.
I found 2 service manuals for cd - players using the CX20108 / CX 20109 / CX 23035 chipsets:
Denon DCD-1700 and Sony CDP-552 ESD. Very different designs for the tracking servo.
But one intersting detail: Sony and Denon installed decoupling capacitors (is this the right term?) between the supply voltage and GND of the ICs mentioned above.
Nakamichi did only use a ferrite bead + decoupling cap for CX23035, nothing else.
I will try decoupling caps on the CX20109/CX2018, maybe I get a slight improvement...
All the best,
Sal
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Old 9th January 2010, 03:28 PM   #18
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Going back to your earlier question- The 'eye pattern' output of the laser on the OMS-5/7 should look UNUSUALLY clean, cleaner than you'll see on any other player. To acheive this, first & foremost you have to do as I mentioned in your other thread, measure BOTH the optical power output AND the laser current draw. If you can't get 0.24mW without exceeding the rated current by more than maybe 15-20%, or can't get above 0.20mW without exceeding the current spec by much, you WON'T be able to get solid performance, and won't be able to use that laser. Also, as I said in a previous post, assuming you do the above successfully, you need to do the servo alignments on MANY different cd's, NOT just a test cd, nor just a few cd's. You HAVE TO align for best compromise settings among at LEAST a dozen different cd's, if not 2 or 3 dozen. TRUST ME; I've service these players since they first came out, as a Nak warranty tech for many years. I know them like the back of my hand.
If you get the laser output properly adjusted & it's reasonably close to output & current specs, but still can't get clean eye pattern on the scope, go back to the mechanical optical alignments & make damn sure you have it idealised.
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Old 9th January 2010, 03:57 PM   #19
Salar is offline Salar  Germany
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Hello Stephen,
I did already perfect alignment. Laser Power is not in question.
The eyepattern looks as good, (or as worse) as from another player with KSS-240A.
It is only a question of going beyond proper setup.
Do you have any idea, why Sony and Denon used decoupling capacitors between VDD and GND for the CX-20108/20109 chips and Nakamichi did not? Did Nakamichi miss something, or ist there only a theoretical benefit from decoupling in thi relatively slow layout ?

Oh, btw, the sled motor is not produced any more, manufacturer is Copal.
Any idea for replacement?
Spindle motor is still produced, Mabuchi RF-310T-11400. It has a longer shaft nowadays, . Instead of cutting the shaft, I had a brass spacer milled with an additional bronce bearing. Works perfect.
All the best,
Salar
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