[dsavitsk]

Sigh.

Well, it is all together, voltages seem to check out (5v on the host pin, and regulated voltages as they should be), but the computer does not detect the device. Does anyone have any suggestions what would cause this, and what I should look for?

 

[ATAT]

When working with Guzzler's DIY DAC (rev A) I had this happen via bad solder joint.. could be that.

 

[dsavitsk]

No, don't think so.

I do think I may have found a bug. Whether it is the bug, and whether it is fixable, remains to be seen.

I have the 1.5K pullup resistor from D+ going to ground. It should go to 3.3V. I should be able to fix that by cutting a trace and running a little wire to somewhere. Further, the datsheet says that this should only be powered while the DAC is conected. In other words, don't provide power to the pullup unless there is a usb device plugged in.

So, assuming I am right that this is the problem, any suggestions where to run the wire? It need 3.3V, and since host provides 5, this is too high (can anyone confirm that using host directly is too high?) But, if I power from one of the 3.3v connections, it creates a real pain in turning on/turning off. Any suggestions?

 

[dsavitsk]

well, i cut the trace from the pullup to ground and stuck a ferrite in between the resistor and the 3.3 power rail near it thus providing 3.3v as required. the computer still does not detect it. Now the question is whether it is not detecting because there is something else wrong, because this is still not right, or because the chip is toasted...

 

[dsavitsk]

I got the following error from a compuer when I plugged it in:

The installation failed because a function driver was not specified for this device.

This seems to be (and this is so predictable, really) a poorly documented windows error. I am sure it means that there is somethig wrong with either the chip, or the way the chip is connected, but i'd like to figure out which one before I take a butane torch to the chip to remove it.

 

[Francis_Vaughan]

This does sound rather odd. You have tried powering it up when it is already attached to the USB host? Sounds as if the DAC is not identifying itself correctly.

The explanation of the reason for the restriction on power to D+ is at best cryptic:
To avoid back voltage in self-powered operation, the device must not provide power to the pullup
resistor on D+ while VBUS of the USB port is inactive.
What I can't quite fathom is that the 2702, which is very similar, works fine without this curious restriction, and an otherwise identical USB input circuit. They just pull D+ up to 3.3v with a 1.5k Ohm resistor.

 

[Francis_Vaughan]

You have the TEST and SSPNED pins run via a resistor to 3.3v. This is a little odd, the application sheets show these tied directly to 3.3v.

 

[DaKi][er]

Might seem a little silly but double check the D+ and D- are going to the right spot, I got them around the wrong way on my dac and spent a few hours troubleshooting that problem

 

[dsavitsk]

Quote:

Originally Posted by Francis_Vaughan This does sound rather odd. You have tried powering it up when it is already attached to the USB host?

I've tried every order of hookup with a bunch of different computers.

Quote:

Originally Posted by Francis_Vaughan The explanation of the reason for the restriction on power to D+ is at best cryptic: To avoid back voltage in self-powered operation, the device must not provide power to the pullup resistor on D+ while VBUS of the USB port is inactive. What I can't quite fathom is that the 2702, which is very similar, works fine without this curious restriction, and an otherwise identical USB input circuit. They just pull D+ up to 3.3v with a 1.5k Ohm resistor.

Yeah, I think I am going to give TI a call and see if they can explain this. I have seen plenty of people use this chip successfully, and no one has ever mentioned this cryptic line.

Quote:

Originally Posted by Francis_Vaughan You have the TEST and SSPNED pins run via a resistor to 3.3v. This is a little odd, the application sheets show these tied directly to 3.3v.

It's a cap and a ferrite.

Quote:

Originally Posted by DaKi [er]Might seem a little silly but double check the D+ and D- are going to the right spot, I got them around the wrong way on my dac and spent a few hours troubleshooting that problem

Doesn't seem silly to me. These got moved around so much that it would not surprise me if they were backwards. I just copied which pin was D+ and which was D- on the USB connection from one of guzzler's layouts with the pcm2902. That chips orientation of the D+ and D- pins are opposite to the 2707, however, so maybe I reversed things too many times.

Would anyone happen to have a definitive pin diagramfor USB jacks? I never have been able to find one and, as I say, simply used gus's.

I think the important lessons here are two fold: 1) put the surface mount chip on the bottom of the board so you can get to it once everything else is populated, and 2) don't solder down everything else until you know it works. At least I put the TDA1543 in a socket so I didn't lose that.

-d

 

[tangent]

Quote:

Originally Posted by dsavitsk I think the important lessons here are two fold

...and use ExpressSCH to draw the schematic, so the board is linked to the schematic, so you can verify your connections automatically.

 

[dsavitsk]

Quote:

Originally Posted by tangent ...and use ExpressSCH to draw the schematic, so the board is linked to the schematic, so you can verify your connections automatically.

Well, D+ and D- aren't reversed exactly, but the pullup is on the wrong one. A bit of delicate surgery removed the resistor and ferite on D-, and used a 1.5K resistor to bridge the 22R resistor on D+ to the 3.3v power trace right next to it. Not ideal, but not too bad either.

Edit: we have music!

 

[dsavitsk]

double

 

[Francis_Vaughan]

Quote:

Edit: we have music!

Excellent!!!

So, how does it sound?

 

[dsavitsk]

Quote:

Originally Posted by Francis_Vaughan So, how does it sound?

Isn't the rule that you aren't supposed to review your own stuff? Nuts to that.

Compared to myusb->spdif converter running into a diyparadise tda1543 dac, even not burned in it is quite a step up. That setup was, in turn, quite a step up from guzzler's 2702 based dac (sorry gus.) So, for the fact that the parts are under $50, it sounds great (though there is a bit of a cheat -- I am using about $90 in jupiter coupling caps that I picked up for another project rather than the $4 in blackgates that have yet to arrive, so that helps a bit.)

Thanks again for your help. I don't think this would have gotten done without it.

-d

 

[guzzler]

Quote:

Originally Posted by dsavitsk That setup was, in turn, quite a step up from guzzler's 2702 based dac (sorry gus.)

No worries

glad to hear that's it's working. It's never a nice feeling when it doesn't work as expected, but luckily an easy fix (as per the PCM2902 boards!). Look forward to seeing it in a matching wooden case as well...