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Old 3rd August 2014, 10:53 AM   #1
svs88 is offline svs88  Finland
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Default Lite DAC-AH distortion repair

Hi there,

I got faulty Lite DAC-AH on my hands and now i am trying to repair it.
The problem is that it gives a lot of distortion (like bad signal on radios). Issue is with coaxial and also with optical input so the problem is not there. Also the distortion is same on both channels so i quess its not issue with op-amp circuit.

Measured all regulator output and they seem to be ok. Fixed the common issue with wrong resistors and adjusted TDA1543 dac chip outputs to correct 3.3V. Did not solve the problem.

Heres the circuit:
http://www.audiodesignguide.com/DAC/...ircuit_new.JPG

What to do next? If one of the eight TDA1543 chips are bad, could that add distortion to the signal?

Thanks in advance.

-Samu
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Old 3rd August 2014, 11:02 AM   #2
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Lots of distortion affecting both channels sounds more likely to come from the digital receiver not locking properly. Do you have an oscilloscope? If so it would be worth checking the frequency of the word clock when locked to the input.
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Old 3rd August 2014, 11:28 AM   #3
svs88 is offline svs88  Finland
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Hi abraxalito! Thanks for fast answer.

Yes i have oscilloscope. How i can check that?
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Old 3rd August 2014, 11:33 AM   #4
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Pin 2 of the TDA1543s is the word select - look for 44.1kHz on here with stable edges. If the edges of the squarewave move around there's a problem with the receiver IC. (I'm assuming you're feeding the DAC from a CD player).
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Old 3rd August 2014, 11:39 AM   #5
svs88 is offline svs88  Finland
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Currently running it with PC. Ill check that later today, thanks again!
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Old 3rd August 2014, 02:07 PM   #6
svs88 is offline svs88  Finland
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See the attachement, looks ok to me..? not accurate scope enough?
Attached Images
File Type: jpg 44_1_khz.jpg (297.9 KB, 59 views)

Last edited by svs88; 3rd August 2014 at 02:16 PM.
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Old 3rd August 2014, 03:05 PM   #7
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Was it sounding normal and one day suddenly became distorted?

I read about someone trying to install OPA627 once in a Lite DAC and it resulted in "lots of distortion" iirc.
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Old 3rd August 2014, 03:07 PM   #8
svs88 is offline svs88  Finland
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Bought one broken while ago and now started to fix it. This seems to have ad847jn opas.
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Old 3rd August 2014, 03:31 PM   #9
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Mine had AD847 as well.

Does the distortion turn on and off when you flick the optical / coax switch?

It could be the optical / coax chip or a toasted DAC chip, try measuring all eight maybe?
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Last edited by Kastor L; 3rd August 2014 at 03:38 PM.
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Old 3rd August 2014, 03:54 PM   #10
svs88 is offline svs88  Finland
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Quote:
Originally Posted by Kastor L View Post
Mine had AD847 as well.

Does the distortion turn on and off when you flick the optical / coax switch?

It could be the optical / coax chip or a toasted DAC chip, try measuring all eight maybe?
Without cable i can hear very high tone, definately not should be there but distortion ends.

DAC chips are in parellar so i quess it is impossible to diagnose those without removing them one by one?

EDIT: Also when i start to play music the distortion sound increases a lot.

EDIT2: Interesting.. DAC chip that is second from top (near to trimpot, see image below) is quite hotter than others.. is this normal?
http://www.diygene.com/store/image/c...-1600x1200.jpg

Last edited by svs88; 3rd August 2014 at 04:02 PM.
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