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HELP!
I have a Buffalo III DAC with a Legato i/v with SE output buffers, which has been working perfectly, but has just stopped working.
I am using the Buffalo with some other DACs with a Minishark to create a DSP version of Siegfried Linkwitzs ASP for LX521 speakers. The other DACS buffers were being powered by another bipolar supply that was causing problems, so I played about with the +/-15 volt supply to the Legato and now the Buffalo has stopped working.
5v is present on the input power of the DAC. I have Paul Hynes regulators in place of Tridents and they are all producing the correct voltages. I can also see the correct frequencies on the I2s inputs for the DAC.
The Legato relay clicks when I apply power and I can feel heat from the resistors on the board. not sure if this is relevant, but the lowest DC off-set I can obtain on the balanced outputs is 22mv with the balanced trim pot maxed out and clicking when i turn it. I can get 0v DC off-set on the SE outputs using the 2nd trim pot.
Please can someone help me to trouble shoot this problem and work out what has happened.
cheers in advance
Brad
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I don't have an led fitted, but I cannot see any voltage on the led connections on my dmm
Brad
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When it stopped working, what was going on? It was playing and suddenly stopped, or had been off for a while and would not turn on, or maybe you were making some changes recently? Just trying to figure out the type of failure-mode we are looking for.
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Hi Brian,
it was working.
I had been messing about with the power supply for the Legato and had removed the DAC from the i/v stage in order to get to the power connectors.
I have tried everything I can think of.
Brad
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Try measure the output of the 3 Tridents.
Careful! Don't let the probe slip.
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It is hopefully just something simple that happened in the deconstruction/reconstruction.
Can you post a few pictures? hopefully we can spot the issue.
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all of the power modules are working and producing the correct output voltages.
hopefully these pictures are ok. the camera on my phone does not do macro very well.
I2S inputs are measuring the correct frequencies as per the outputs on the MiniShark. very confusing.
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I don't think that I have access to the album and photo gallery feature, so cannot upload any pictures at the moment.
Brad
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Click the Attach button at the top of one of your posts to attach pictures /\ . Edited by user Friday, October 24, 2014 11:30:36 AM(UTC)
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cheers Brian, File Attachment(s):  WP_20131222_010.jpg (320kb) downloaded 1 time(s). WP_20131222_004.jpg (285kb) downloaded 0 time(s).gl51otk attached the following image(s): WP_20131222_008.jpg (249kb) downloaded 24 time(s). WP_20131222_006.jpg (251kb) downloaded 23 time(s).You cannot view/download attachments. Try to login or register.
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more gl51otk attached the following image(s): WP_20131222_008.jpg (249kb) downloaded 13 time(s). WP_20131222_006.jpg (251kb) downloaded 15 time(s).You cannot view/download attachments. Try to login or register.
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Hi Brian,
looks like I may have found the problem.
I retested everything and ended up measuring the regulator voltages again. I'm getting 5v output on the VDD_XO reg.
I will get a replacement regulator sorted. hopefully this will not have damaged the DAC, or clock.
Brad
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ok.
I have just replaced that broken Paul Hynes regulator with a spare DEXA 3.3v regulator. I am now getting 3.3v on the VDD_XO output, but the DAC is still not working.
my DMM on the lock light is measuring 0v and there is no output. has the 5v output on the broken regulator damaged the clock?
is there anywhere I can test the clock output? I have a frequency test probe on my DMM.
Brad
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Do you measure any voltage at the MUTE led?
If your meter can handle 100MHz, you should be able to probe for XO output.
You may very likely have a dead XO though.
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cheers Brian,
my dmm only measures up to 15mhz!!
the mute LED pins are measuring 3.27v
Brad
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Arghhhh
Tried to fit a new 100mhz clock and ripped up the trace that feeds the clock to the dac chip. Looks like I can salvage it with a magnifying glass, epoxy and patience, but its a right pain.
To save me time, does anyone know if I can test the dac using a 11.286mhz clock?.
Also I need to know where the three smd capacitors that sit alongside the clock trace go. Want to check to make sure o haven't damaged anything else.
Brad
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You will need at least double that clock speed for PCM source and triple for SPDIF. Very sorry for the misfortune.
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Nightmare.
May be easier to just buy another dac.
Could then go dual mono when I sort out the broken one.
Couple of questions
How quickly can I get either a b3, or b3se
Can I do a dual mono with a b3 and a b3se, or is it best to use 2 x b3
Can I get away with std legato values when going dual mono. Happy with higher db gain with dual mono, but want to operate in spec
Brad
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I would use two B3SE or two B3 I would personally not mix them - though technically it would work fine. Yes - you can use a single Legato - the standard values will work fine - but you will have higher than normal output. Edited by user Wednesday, November 12, 2014 5:41:37 PM(UTC)
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 1 user thanked Russ White for this useful post.
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