Quote:
Hi,
It was the first time I did some SMD soldering, so don't be upset with the results. I resoldered U9 on the backside, but it didn't help. I did't want to touch the chips on the front side without your advice, because I had a lot of trouble soldering them (which you can see on the right hand side of PCM1794). Therefore I used a minimum amount of solder on the left side, but I measured through the legs at the top to their corresponding contact point somewhere else on the board and they "seemed" to have contact. If you say I should solder them again I will do so, but I did not want to make a bigger mess than it already is. Hope the picture quality is good enough, I didn't get them "sharper".
Thanks for you help guys!
https://imageshack.us/a/img690/8963/img20130602121140.jpg
https://imageshack.us/a/img208/6914/img20130602121204.jpg
I can't find anything amiss, except around the bottom right of the DAC chip. At least from these photos, it appears you did very well, indeed, for a first time soldering SMD!
Here's the situation - if a PC recognizes the device, but no sound output occurs, and all the voltages check out, then there has to be an issue in three possible places:
- Connections between the PCM2707 and the PCM1794,
- Connections from the output (analog music) side of the PCM1794, or
- Connections from the analog (music) output of the pupDAC.
Of these, I would ordinarily tend to discount #1. The reason being, first - your solder work looks fine on the PCM2707 chip and on the left side of the PCM1794. Second, chances are if there was some issue in the connection between the two DAC chips, the PCM2707 would show some sort of error, too, and not be fully recognized by a PC.
That said, one might make the case there's a fundamental issue with the connections between the two PCM chips. Otherwise, you might get partial sound, static, or some other indication of an incomplete connection. If you can't hear anything anywhere, then the issue may be more fundamental and it could be the connections between the PCM chips. There are four of those - one is quite obvious and is the trace from the 4th pin from top right on the PCM2707 to the 4th pin from top left on the PCM1794. The other three pass through vias to the bottom of the PCB and then connect to the left side of the PCM1794. These pins are the first 3 pins on the top left of the PCM2707 and they connect to the 5th, 6th, and 7th pins from top left of the PCM1794. IOW, the 4th, 5th, 6th, and 7th pins from top left on the PCM1794 are all of the connections between the PCM2707 and PCM1794. Check those pins with your DMM and see if you can measure -0- resistance between them and their corresponding connections to the PCM2707. If not, then you may need to re-flow the PCM1794 pins and even the PCM2707 chip, even though it looks good from the photos.
That leaves either #2 or #3. I would ordinarily discount #3, because it appears the soldering you've done on the opamp looks fine. Certainly, there's plenty of room around the pins to determine whether you've got good connections or not. If you can verify the traces from the tops of the pins to the traces, then I don't think there's an issue. Still, it would help to check every SMD part. Remember that capacitors left unsoldered may affect performance, but I doubt seriously they would cause the device not to work. Resistors and ferrites, on the other hand, have to be soldered on both sides or there is an actual break in the circuit.
If nothing else checks out so far, then that leaves the right side of the PCM1794 chip. It's hard to tell for sure, but there may be a bridge between the bottom two pins on the right side. If that checks out OK (look for zero resistance between the two pins to confirm a bridge), then verify connection from the pins to the traces for the most important pins for the audio output - the 3rd and 4th pins from the top right, and the 3rd and 4th pins from the bottom right. Those pins are the balanced current outputs for the Left and Right channels of the DAC.
One thing to look for when you measure with the DMM - it may be that you're pressing down on the DAC pin and the force is enough to make the pin have contact with the trace beneath, but without that force, the pin is not really making contact with the pad.
It will be difficult - but I would try re-flowing the pins on the right side. Note that I said - re-flow - not add solder. I don't think the addition of solder is going to help on the right side - it looks like the solder quantity is sufficient. What you want to do instead is make sure you apply enough heat that the solder joints are "smoothed" compared to what they look like right now. Extra flux will help with that, but not more solder. In particular, you want to be certain that the tips of the pins have been heated next to the pads. If there's any solder at all there, then that should establish the proper connections. At the same time, ensure that your soldering iron is clean (and stays that way), and it should "suck up" any bridges between the pins.
It can be tough to find the answer in a situation like this. I have the same problem with one that I have at home - I've built about 10 right now and they all worked out of the chute, but one is a problem that I can't solve. If you reach that point, it may be that the DAC chip needs replacement.
