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Naim NACD 3.5 repair

K

kiran1103

Active Member
Hi Folks,

Got a CD3.5 from previous owner who had no history. It did not have a cd puck so after waiting for 10 days finally got it. But the original issue was disc tries to spin and the dreaded ERR msg. It doesnt even read TOC. I checked for red laser and its present. The lens bobs up and down for 4-5 times and then this ERR meggage. I dont know if its laser or someting else. In an attempt to check voltages from Lm317, I checked the first from left when the unit is facing towards me. It showed 21v something. I moved to second one and it was around same but when removing the pin grabber, I forgot to switch off the unit and I think I shorted the pins. Now the motor spins insanely fast. Its very high speed. From reading it seems the clock circuit might be gone. I removed the three LM317 out of circuit and tested with Peak LCR meter. All show as Dual LED something. I thought it was a transistor but I may be wrong. What would be my next steps to check? Did I damage the servo chip or something? Or should I order 6 LM317s and replace them. I dont think all of the LM317 would have been gone. Thoughts? After I fix this then I will move onto the laser issue.
 
Ok, having not played with one of these in at least 15years...:

Things that will kill the clock signal/lose control of the CD speed: damage to oscillator; damage to the Dac; damage to the CD servo.

There are several key things about the CD3.5; its based on a CD12.5 CD mechanism, teh CD servo & decoder is SAA7335 ( I think), on the underside of the PCB. The Dac is a TDA1305, again, on the underside of the pcb; and the dac is fed a clock generated by an adjacent 74HU74 inverter, again, on the underside of the board. The inverter is used as a classic 'Pierce' crystal oscillator with 16.93Mhz quartz oscillator; the TDA1305 vi pin 16 (iirc) then sends the clock signal elsewhere on the board, primarily - to the CD servo.

There are separate voltage regulators for
  1. each of the output channels,
  2. the CD decoder,
  3. the electronics in the CD tray (laser mech and its driver circuit);
  4. the TA1305 dac;
  5. the 74xxxx inverter
- and a couple of other functional things, like the Naim control eeprom and front panel.

So far so, good: so the thing to check is voltages on all the voltage regulators. The safe way to do this with LM317s is to ground the 0v pin of your voltmeter, like the ground plane, or the screw bonding the green/yeool earth wire to the case - and just probe the bare metal of the fixing tabs of the regulators with the other lead

If you can do that, plotted on a graphical sketch of the PCB looking top-down (however simple) - we can go from there.

Good hunting!
 
Martin,

Thank you for the detailed explanation and clear instructions. I have measured them and attached them as images. Most of them measure 3.8, 5.0 and 25.0 except two which measure 3.7, 9.5 and 8.2 and 9.5. These are all of the main board. I had to remove the ribbon as the cd motor was spinning insanely fast. I read somewhere that the laser mechanism also has one Lm317 so will check that in evening and report back. Thank you again

https://imgur.com/PfOaMZU

https://imgur.com/UMmAkpp
 
Also one more data point. I did not put the link plug behind. Not sure if it will change any voltages I already measured
 
kiran1103 said:
Also one more data point. I did not put the link plug behind. Not sure if it will change any voltages I already measured
Click to expand...
That link plug only connects the two regulators, one for each channel of the output stage, to the raw c 25vdc supply.
It'll have NO bearing on what is Rong.

Thanks for the diagram - will have a think...
 
Well those voltages are all good, to my eye.
You need to trace the IC which is fed from the output of the second-from-left regulator you think you shorted. it is reading 5v on test, so the regulator survive d; I fear whatever it feeds got hit by the +24v raw supply.

Since the dac and clock are fed by the two regs near the little oval silver crystal case in the middle of the board (which both appear to be correct) - I fear you've fried the SAA7345 cd servo.

Check what the suspect reg feeds; after that you will need an oscilloscope to test much further.
 
Thanks Martin. I will have a check and report. As you said it would have fed full 24dc raw output to whenever it’s tracing. The SA chip seems to be smd type and no way it’s possible to replace it. Hope for some good luck. Thanks
 
No luck. I traced all the components from the 2nd reg to saa7376GP chip . I replaced lm317 of that particular on that shorted and same results. The motor is still at full speed. Tested vdc of all pins where the ribbon is connected and didn’t see anything more than 3v. Any other components to check. I have an oscilloscope but still learning on how to use it. But some high level steps I can figure out and learn. Thank you
 
Last edited:
Well - bugger.

If you have a modern digital scope, you can probably then set most thing to 'automatic' and just go probing - see the last couple of pages on the adjacent thread: https://pinkfishmedia.net/forum/threads/naim-cdi-no-sound-output.293104/

I would look for 1. The clock signal on pin 13 of the SAA part, relative to 0v - it'll appear a square-ish waveform at 16.899 MHz.
If you see that even briefly, the clock is good, the dac is almost certainly good, and the servo -dead.

So - likely worst news, but take heart - i once killed the oldest of my 3.5s in exactly the same way!
( I kept it for spares to feed another, never used, so eventually culled the transformer and transport for spares - the VAM1250 is impossible to find now, and of use to anyone with a CD3.5, 5. CDX. CDX2, CDS2, and a few later models besides... don;t throw it away.)
 
Thanks Martin. Thinking the worst I ordered a chip from Poland. He claims it’s original but worth the try. I will try the probing just to confirm that Saa chip is cooked.

www.ebay.com

[1pcs] SAA7376GP Digital Servo Processor QFP64 | eBay

MPN: SAA7376GP. Case: QFP64. Digital Servo Processor.
www.ebay.com

Btw the original issue was half spin and ERR message so the transport is gone too. If I succeed here then move onto the laser
 
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