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GrubDac assistance please! - Page 2

post #16 of 48
Unlikely, but you never know. I would be more suspect of your cable attachment. The signal integrity may be marginal at J2. Any intermittent signal would prevent it from being consistently recognized. Did you provide any strain relief on the cable itself? Does a cable reposition and/or wiggle make any difference?

I would take your multimeter and check continuity through the cable, but, measure on the board at J1. All the signals at J2 are tied to the same signals at J1. This will give you a better idea of the integrity of J2.

You may also want to just rework the J2 end of the cable again. Clip off a 1/2 inch and start again. After all the gyration, there might be stress damage to the wires. Be sure to strain relief the J2 end when you think it is good to go.

BTW, I think you should also follow TomB's advice and cross post a link to this thread in the main grubDAC thread. It would be nice to get cobaltmute's take on the situation as he is the designer and grubDAC expert. He will certainly be able to take you fully through the design and inner workings far better than I could ever attempt to do.
post #17 of 48
Thread Starter 

Cable wiggles didn't seem to make a difference but I went ahead and replaced the cable.  No change.  :(

No detection at all.. not even a chime.

Posted a link in the regular GrubDac thread for Cobaltmute.  Good advice so far and thanks for staying with me on this.

post #18 of 48
Can you post some updated pictures as well? Just of DAC1 as DAC2 appears to be fine now.
post #19 of 48
Thread Starter 




Ha!  Not as pretty as it once was, no?  Too much fussin' perhaps.  ;)


When I desoldered the HOST and VCCP pins from each other the computer makes a detection noise once again... although there is not music and the computer's onboard sound card continues to play.


I've been playing around with the relationship of the HOST and VCCP pins to try and see what is happening there and the schematics I read of Erik's (  http://www.diyforums.org/GrubDAC/schematic/GrubDACschematic.pdf ) and TI's (  )

seem quite different.  Erik's has them connected and TI's they are not.  Also, the hole (is there a technical name for these?) (Which is now seperated as shown in photo) at the very edge of VCCP is hot at 3.3v which I find confusing when referencing either schematic.


Beleive it or not, none of the three pins in the upper left are connected(verified by meter) and none of the three are connected to the 3.3v hold by

the VCCP pin currently.


Happy to solder jump... run jumper wires...fill in holes... run around in circles.  You name it and I'll try it.  :)


post #20 of 48
Okay, that appears to be a problem. Pin 2, VCCP, should be tied to the "hole" or via directly next to it. In other words, the via provides 3.3V to VCCP. Pin 3 should be tied to pin 2, thereby providing 3.3V to both pins.
post #21 of 48

Ok, I don't know if it my sinuses or work stress, but I'm not really making out where we are are.


DAC2 is working?


DAC1 is working on laptop only, but not desk machine?


Is there an amp involved afterwards?

post #22 of 48
Thread Starter 



Tied pins 2, 3 and the 3.3v hole back together once again.  Tested while running and it measure 3.3v as it should for the whole junction.

Still working on laptop and not on the desktop.  Tried restarting the desktop but no change.



DAC2 is working, yes.

Correct, DAC1 works on the laptop but not on the desktop machine.

Amp for the laptop is a Trends 10.1 and some powered Swans M200 at the desktop.

post #23 of 48
Just to be clear, when you switch between DACs, you are using the same USB jack on the desktop computer? Are you going straight into the computer or are you using a USB hub? The cables you made for each of the DACs, are they each the same type and about the same length?

Can you verify Pin 1 of U1 (PGND) is actually still tied to ground (measure to be at ground reference)?
post #24 of 48
Thread Starter 

Yes, same USB jack on desktop computer.. straight into the computer (no hub).  Same type and length of USB cable for each DAC.  I even tried another brand USB cable as noted before.

PGND is grounded to the 0V input/wire.

post #25 of 48

From your last picture, are Pin 2 and Pin 3 on the PCM 2706 (the dot indicates pin 1) connected?  Pin 3 is HOST detection (to see that the USB is connected) and Pin 2 is power.

post #26 of 48
Thread Starter 

Unlike it shows in the last picure, Pins 2 and 3 are now connected again.

post #27 of 48
So, I am thinking you should use the fact you have two grubDACs to your advantage.

Hook DAC2 up to the desktop, measure all the connected pins on U1 (per the schematic) and post those values.

Hook DAC1 up and do the same.

Let's see what the differences are between the two units.
post #28 of 48
Thread Starter 

Brilliant idea jdkJake!  I'll get back with you soon.

post #29 of 48
Thread Starter 

What shall I measure btw?

Voltage in reference to ground (+0)?

Resistance to ground?



post #30 of 48

Voltage to ground will be the most useful as long as you're careful.  It's could be a bit risky when the power is on, though.


What I've found is very useful is to measure resistance for continuity (zero resistance) between the pins on the IC chips and the terminus of the next part when following the trace.  So for instance, with the power off, put one probe on a pin of an IC.  Follow the trace that pin is connected to and place the other probe on the first part that's connected to that trace.  If you get zero resistance, you have full continuity to that pin.  Next, keep the probe on the part but move your other probe from the first pin to the pin next to it - if you still get zero resistance, that means you have a bridge in the pins.  If the resistance is not zero and is supposed to be that way, then unless they're connected to ground, you should get something different each time - you can use that to compare to your working GrubDAC.  Just a suggestion and one that has no risk because you do this with the power off.


Jake has been doing a great job in helping you and if you are careful - proceed with his suggestions.  As stated above, I would think voltage to ground is what you want to measure with the power on.

Edited by tomb - 1/11/11 at 9:42pm
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