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Old 25th February 2012, 01:17 PM   #1
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Default Naim CD1 with no audio output.

Hi.

I am asking for a push in the right direction. My Naim CD1 has stopped sending out any audio (both channels) everything else work ok.

I have done some measurements:

No output ( 0 volt ) from the DAC (TDA1541A S1) pin 6 and 25

Power looks good. Pin 28 +5V, Pin 26 -5V and pin 15 -15V

Clock looks good. BCK 5.6MHz and SCK also 5.6MHz

LE/WS toggle every 16 clocks

There is data activity on pin 3

So I have replaced the DAC with a new one (Seller said it was new and unused so I payed big $$$$) but the replacement did not bring any audio out from the DAC.
So now I am a bit locked up. Can someone give me a hint on what to do next ?
Thanks in advance
/Jens
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Old 26th February 2012, 01:28 AM   #2
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analog-out muting may be on...or faulty
do you get any S/PDIF out?

Boky
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Old 26th February 2012, 06:56 AM   #3
Mooly is offline Mooly  United Kingdom
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It's never the big chip

The data sheets shows this to be current output DAC. That means that the output on pins 6 and 25 isn't visible on a scope as it will be fed into a virtual earth amp (opamp). So you need to trace where pins 6 and 25 go (almost certainly to an inverting input pin on an opamp) and you need to scope the output pin of that opamp to see if any audio is present.
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Old 26th February 2012, 07:56 AM   #4
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Boky:

Naim CD1 dosn't seem to have a S/PDIF output, so I don't think there is any analog mute !!! I may be wrong.

Mooly:

Good point. I have not seen that. The outputs are easy to trace. I will make some measurements and return.

Thanks to both of you.

/Jens
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Old 26th February 2012, 10:46 AM   #5
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Quote:

So I have replaced the DAC with a new one (Seller said it was new and unused so I payed big $$$$) but the replacement did not bring any audio out from the DAC.
So now I am a bit locked up. Can someone give me a hint on what to do next ?
Thanks in advance
/Jens
I hope it wasn't an S1 double crown TDA1541A you removed? Might be wise reinstating it if you trace the problem to elsewhere.
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Old 26th February 2012, 12:06 PM   #6
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I would suspect the Opamps... DAC output is practically zero if the I/V opamp works corectly - you should see voltage at the output pin of the first OpAmp.
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Old 27th February 2012, 12:35 PM   #7
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Yes is was the S1 double crown.

Have done some more measurements:

Output from DAC goes to pin 2 of a opamp (OP42)
Power on OP42 looks ok (+17.6V and -17.6V)
No AC output on pin 6 (checked with scope when CD is playing/spinning) there is about 3-4V DC, same on both channels.

Output from first opamp goes via a Reed-relay to the next opamp (also a OP42), but the relay is not activated (open). Both relays (right and left channel) seems to be controlled by the DEEM signal, via a couple of transistors, from the SAA7310GP controller, the DEEM signal (pin 41) is always LOW

Any suggestions ?

/JJ
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Old 27th February 2012, 01:32 PM   #8
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Yes, that's exactly right. That first reed-relay is the CD deemphasis circuit, activated by a flag from SAA7220. It is normally -open, and only switches the extra RC components into circuit when HF demph is required. So your check shows it is probably ok.

This relay never breaks the continuity between the IV stage and next opamp.

Afterthought: check all the polystyrene caps have not gone 'short circuit'. A moments carelessness with the iron will melt them (perhaps when replacing the dac, and that will hold the audio signal to ground since there's an RC filter after each of the first two opamps in the output circuit (as part of 3rd order Sallen-Key filter design)
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Old 27th February 2012, 02:07 PM   #9
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Thanks Martin.
All poly-caps checked, no shorts.

No signal after first opamp, on both left and right channel.
The failure occured suddenly. One day the player was ok, and the next day it dosn't work, and has not worked since.

Is it possible to find a circuit diagram anywhere on the Internet ?

I really don't know what to do

/JJ
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Old 27th February 2012, 03:29 PM   #10
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Pulled the TDA1541 out.
Injected a 1KHz 0.1Vpp signal at the DAC pin 6 and 25 on the PCB. That gave me a very nice 1KHz to be measured at the output connector

So the failure must be between the drive and the DAC...... I think

Any suggestions ? Things to try ?

/Jens
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