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RichG  
#1 Posted : Monday, January 27, 2014 1:07:36 PM(UTC)
RichG

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United Kingdom

Hi,

For a while I've been having an intermittent issue with my Buff2 build. I have an OTTO II which switches between a
4:1 SPDIF MUX and an Amanero USB to I2S. Usually this all works very well but from time to time the Amanero signal has played up and failed to provide a 'sync'able signal to the Bufalo. I had thought that this was a connection issue and had previously reworked the (very short) wiring and this appeared to 'fix' the problem.

However, over this weekend the Amanero completely stopped working. The driver showed no problems connecting on both Windows and Linux so presumed it to be a hardware issue.

Checked all the connections which seemed OK.

Connected my scope and it was apparent that the Amanero signals for BCLK and DATA were at a much lower level (less than 0.5v p to p) than the FSCLK signals or any of the signals from the MUX (which were all around 3v ptp).

Connecting the Amanero directly to the Buff (bypassing the OTTO) restored a good level on all the signals and the DAC sync'd fine.

Thought maybe there was a solder bridge or some other short causing the problem but close inspection shows nothing I can see.

Metering the two inputs used for the Amanero BCLK and DATA and they appear to have a very low DC resistance (33R and 38R) compared to the others (all approx. 47K). I removed the resistors on those inputs and still get the same very low reading.

Looks to me like the two inputs to the logic chip are faulty....

Is this a sensible conclusion? Is this a normal failure mode for the chip?

Also, any ideas how I might fix this? Do I need to replace the whole OTTO II? Normally I'd be fairly comfortable replacing the surface mount chip, but in this case I'd have to remove the connector blocks and the resistors to be able to get clear access, so it's going to be a right nuisance.

Thanks for any help.
Richard
Russ White  
#2 Posted : Tuesday, January 28, 2014 10:21:27 PM(UTC)
Russ White

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I have not had one fail, so I can't really be sure.

Things that could cause one to fail would be ESD at the inputs or a signal that exceeds VDD beyond the rated level.

You could try replacing the chip, but it may be difficult enough to warrent just replacing it if you determine it is truly damaged.

Sorry for the bad luck.

Cheers!
Russ
RichG  
#3 Posted : Wednesday, January 29, 2014 11:56:51 AM(UTC)
RichG

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Joined: 1/27/2014(UTC)
Posts: 2
United Kingdom

Originally Posted by: Russ White Go to Quoted Post
I have not had one fail, so I can't really be sure.

Things that could cause one to fail would be ESD at the inputs or a signal that exceeds VDD beyond the rated level.

You could try replacing the chip, but it may be difficult enough to warrent just replacing it if you determine it is truly damaged.

Sorry for the bad luck.

Cheers!
Russ


Thanks Russ,

I imagine you are right about the failure - although I'm generally very careful about excessive levels and ESD. I guess it probably is just bad luck :(

The low resistance / impedance of the failed inputs is a little unexpected - I would have thought the inputs going open circuit would be more likely, but then I've not had much experience with these types of chips.

Cheers
Richard

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