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Old 21st May 2007, 08:04 PM   #1
arupg is offline arupg  Latvia
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Default Aligning Optical lens in a NAD C-540 CDP

I've just installed a NEW laser mechanism unit (complete) in my NAD C-540 CDP and I find it still skips on a few discs. Why is this?? Could the focus be off? If so, how do I set it right?

Anyone with a C-540 service manual? Will appreciate very much for all your kind assistance.

Thanks in advance!!
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Old 29th January 2008, 01:06 PM   #2
PLS is offline PLS  Portugal
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´Hello. You hame a common problem with me and other NAD owners.My C541 exibhits the same issue. First its a fragile pickup and chipset combination from Sanyo. With C541i, NAD evolute to a Sony transport and chipset. They clame evolution to CD-RW compatibility, but Sanyo L9042 is CD-RW ready too! C541 and olders player with Sanyo solution use L9240 which is not CD-RW ready. I advice to boost the +8V power line. It feeds the motor section and +5 Volts digital line. The motor section comprises the pickup coils, pickup motor, disc motor and tray motor! Its a very power hungry line, the JRC 7808 regulator fail to supply a stable 8V output to the motors, specialy in skip operation or more demand error recovery from system.It will afect +5V line with voltage drop and noise, and wihout enough voltage boost, at least +3v from input to output the traditional 7805 wont play at 100%. So I recommend to get low voltage drop and faster 3 Amps diodes for all power supply. get more than the double, triple if possible (10000uF) capacitance at the first electolytic capacytor (NAD use 3300uF), use the original to boost and clean the +8 Volts output before the 7805 regulator. Change the 7808 to a LM350 arrangement with a good heatsink and a regulation of +8,15 V at least. LM350 can manage 3 Amps, and less than 2V drop at 1,5 Amps, so its easy to drive this line, and mantain enough voltage to the 7805 works fine.Get the service manuals at:

http://www.diyaudioprojects.com/Schematics/index.htm

Use good cd-r media (Sony CD-R) recorded at 4x.
This update should improve sound and track ability of original and cd-r media!

Best Regards
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Old 29th January 2008, 03:06 PM   #3
arupg is offline arupg  Latvia
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Thanks for the last post.

But with all these mods, does the NAD CDP work properly or still pose problems in the transport mechanism when either asked to play or >> or << and so on.....

Will appreciate a reply
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Old 29th January 2008, 06:17 PM   #4
PLS is offline PLS  Portugal
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With my C541 i get more stability in playback to shock and to original cd that have some skiping problem. Still scratch disk, lousy media or hig speed recorded media still have problems!
I'll send to you a document to predorm a mod, but i dont think it get better with this mod, the power supply +8V current boost is more efective in my case!

Best Regards
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Old 29th January 2008, 06:41 PM   #5
Eva is offline Eva  Spain
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Some time ago I repaired a Rotel CD player with a similar problem. It had an 8V regulated line that was dropping to 7V or 6V in certain circumstances like outer tracks, scratched discs and sometimes even when first reading the disc. Since the 5V for the chipset were derived from that line and dropping too, the player was hanging and behaving strange and had to be turned off and back on sometimes.

I blamed the power supply at first (naive me), and I built a simple MOSFET low-dropout regulator on vero-board that was able to keep the 8V much more stable but the problem persisted. Current consumption was well over 1A sometimes and now it was the own mains transformer the one not being capable of providing 8V (drop across my ragulator was under 100mV).

I tracked this abnormally high current consumption to the spindle motor. It was definitely faulty, it was drawing a lot of current and exhibiting little torque at times. The poor driver IC was almost cooking too. I replaced this motor and the problem was completely solved. Current consumption was greatly reduced, it never went over 0.5A or so again...

So if your supplies sag, the first thing to check it that your motors are not faulty...
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Old 29th January 2008, 09:20 PM   #6
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Partially shorted spindle motors are not an uncommon problem, look here, section 13.3 and 13.4:
http://www.repairfaq.org/REPAIR/F_cdfaq8.html#CDFAQ_001

(I do recommend the repair FAQs, I think I did read all of them some years ago. Lots of interesting and useful stuff!)
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Old 30th January 2008, 02:55 AM   #7
arupg is offline arupg  Latvia
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PLS, Eva & megajocke :

Thanks for all the posts, again reconfirming that basically the NAD earlier CDPs have their transport sections poorly executed. Unfortunately, their is not much we can do to UNDO poor circuit designs.

Nevertheless, on my NAD C-540, I've replaced the optical mechanism (complete) twice now and this does come with a brand-new spindle motor so I reckon the faulty issue with the motor is here eradicated. But the tracks still skip inspite of the new optics and I wonder whether is it the poor quality optics or lack of drive from the circuits (which is current starved).

And its getting more and more difficult to get hold of the Sanyo SF-P101N 5/8P optical kits as they too are discontinued now.
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Old 30th January 2008, 02:24 PM   #8
PLS is offline PLS  Portugal
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These voltage drop with the Sanyo pick-up chipset solution is well know to NAD project team. Its represented in the service manual a 7,8V and less figure at power supply pins of the ICs that drive the motors, from 7808 regulator.

Even a +7 volts figure or less is able to drive these chips, see the datasheets of these ics, but i really doubt about the cleaness of the supply energy, which must have impact in the all system. I notice a good diference in sound and stability!
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Old 31st January 2008, 05:34 PM   #9
arupg is offline arupg  Latvia
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PLS:

Going by what you recommend for my C-540, I have located the following that needs to be replaced. They are mentioned below:

1. C122
2. C123
3. C124
4. C311

as per the document NAD engineers published claiming that it improves CD playback from "NO DISC" situation.



5. C529 - presently 3300uF,16V. I can replace this by 10,000uF,16V.

6. DIODES: You said "get faster 3 Amps diodes for all power supply".

Can you please tell me which are these diodes ? The part Nos please, if possible? And with what have you replaced yourself ?

Finally, is my playing CDs likely to improve with all these mods ?

Thanks again!! I appreciate you helping me.
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Old 1st February 2008, 09:37 AM   #10
PLS is offline PLS  Portugal
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When you ask for service manual, you should be able to understand whats on the schematic diagram. If you are not prepared to understand the basics you should get support from someone that is used to do this mods. To change the diodes you should pay attention to the component dimension and value rate, for instance, maximum current capability, 3 or more (Amperes) and maximum voltage (At least 50V). You shoul shearch a diode reference with high speed and low voltage drop to improve power supply perfomance at all stages!

Best regards
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