GrubDac Help
Jul 23, 2010 at 6:12 PM Thread Starter Post #1 of 11

Lanning

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So I just finished building my GrubDac, but my computer will not recognize it. However, the led turns on, so it is clearly getting power from the USB. I highlighted some weird looking parts of the board on the photos; please excuse my gross soldering. Does anyone know how I would check through the board to see what is failing? Thanks!, and sorry I can not give more information.
 


 
Jul 23, 2010 at 6:48 PM Post #2 of 11

tomb

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Can you measure 3.3V when you stick a DMM probe in the 3.3V hole and the other probe on 0V?
 
I can't speak for the spot on the right, but the one on the left is a via (place where the trace goes vertical and is continued on the other side of the PCB).  By itself, it's not going to hurt if you get solder there, but it depends on what else it's touching.
 
Just a hint, but you might try cleaning the PCB of all that flux, too.  The pads and pins on some of those parts are small enough to short if there's enough dirt mixed in that flux.
 
Cobaltmute will probably have some more ideas if those don't improve things.
 
Jul 23, 2010 at 8:39 PM Post #4 of 11

jdkJake

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So, I just built one of these today, so, I am far from an expert, yet, it worked, so, that gives me some props... :wink:
 
Your part placement looks good in terms of orientation, I need to check values.
 
My big suspicion is the 2706. You have a LOT of solder on those pins. Remember, just a dab will do ya!  I would go back and heat those joints and try to remove some of the excess solder. I see some potential bridges on a couple of pins. DId you do the "back light" trick on the grubdac site?
 
   http://www.diyforums.org/GrubDAC/GrubDACphoto-build-1.php
 
It REALLY works good. I was able to clear a bridge using this technique. The board is really well designed for this type of examination.
 
BTW, you need to clean your board better. Go to the pharmacy and get some 91% rubbing alcohol and a cheap-a-- nylon toothbrush and scrub hard! makes all the difference!
 
Hope this helps.
 
Jul 23, 2010 at 9:35 PM Post #5 of 11

Lanning

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Thanks for the advice, it was very helpful, but it still will not work. Here is a picture of the board under light, after I removed three solder bridges. It looks ok to me, but maybe some more experienced eyes will spot something wrong. Thanks.
 

 
Jul 23, 2010 at 9:41 PM Post #6 of 11

tomb

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Well, if the 3.3V test point won't work, that often points out that the problem is with the TPS chip on the back (U2).  We can't see it very well from the photos you've supplied so far.  Can you clean that chip up and see if there are any solder bridges/cold solder/no solder etc.?
 
Edit: Actually, from that last photo the PCM and WM chips look relatively OK.
 
Jul 23, 2010 at 10:33 PM Post #8 of 11

cobaltmute

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No power on the 3V3 point means that the regulator has shutdown, likely due to over-current shutdown due to a bridge.
 
Looking at the back-lit version of the board I see two possible bridges on the PCM
 

 
the left one on the pic looks visible on the other pic of the top side as well.  That one will cause a bridge to shut to board down as it is from a power pin to the ground plane.  The one on the right will cause problems as it is on the data lines to the WM8524.
 
Jul 24, 2010 at 3:21 AM Post #10 of 11

Lanning

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You guys are miracle workers, it works like a charm now, after I fixed the 2 solder bridge issues, and cleaned up the soldering mess on U2. Thanks so much for all of your help and time! 
 

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