Film-Tech Forum ARCHIVE: Noise problem on SONY DCP1000

This is topic Noise problem on SONY DCP1000 in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Marin Zorica (Member # 1716) on 09-30-2008, 01:38 PM:

Here is the problem:

One night I did noticed strange noise on L channel, some noise....but sound on L was okay, and during louder parts in movie you can't hear noise because isn't high in level. Than I did go to investigate what is about....everything was normal, also I try to use Lc output but same, even I changed output balanced driver and TL072 and DS e-potmeter before it but same. But I noticed that on AIN (8ch external input card) L and Lc level shows -600dB, where else are -90dB normal....i did unplug card and than noise is gone....I was think is because of bad AIN card....but after some days noise is here again, symptoms same as first time, but noise is quite low now...and noticeable only during silence parts.....

I did plug in AOUT card from another processor and noise is gone....so probably problem is in that card, only thing I didn't change is AD converter CS4328 because I don't have any...but I tested signal path and noise is coming wright on AD output, and normally when I lower master level it gone, but if some signal arrives it appears...it behave like GATE.

Posted by Robert Minichino (Member # 3495) on 09-30-2008, 02:37 PM:

There are on-board voltage regulators (7805/7905) on the AOUT card that power the DACs. I would check the +/- 5V supply to the DACs for noise.

L and Lc also share a DAC (IC10), so it may very well be the DAC.

Posted by Marin Zorica (Member # 1716) on 09-30-2008, 03:35 PM:

I did check voltage, it's normal -5V/5V. So last thing is to check DAC...only I don't have any to replace it.....
Robert, are you maybe know other possibilities of this failure?

Posted by Robert Minichino (Member # 3495) on 09-30-2008, 03:51 PM:

The only other thing on the AOUT card that would produce noise at the DAC output itself other than the DAC and the power supply would be the TDM bus interface. Since you said the noise was low in level this would mean that only the low-order bits are being corrupted, which is an incredibly unlikely way for it to fail.

Posted by Marin Zorica (Member # 1716) on 09-30-2008, 04:10 PM:

Hmmm....strange indead....and bus interface is some pre-programmed mcu??

But other card is working well...so probably is something with AOUT itself?