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The GrubDAC - Page 72

post #1066 of 1073
I can't guarantee anything, but this has been a long standing issue with Win7. There is no difference with respect to 2707 or 2706 for this issue. The 'C' variant is supposed to address it.

As stated however, I can't guarantee anything about your personal setup. I just thought that maybe you could confirm it for all of us.

If you're afraid to mess with it, I can certainly understand.
post #1067 of 1073

Well, this is a first. Never had any sort of problem with SMD soldering before.

The board looks fine, there are no shorts anywhere, I've tested every pn on the ICs and they are soldered properly. The electrolytic caps are soldered right. PC feeds 5.18V into the DAC. The LED lights up as it should.

 

Problem is, the 3.3V test point gives 0.25-0.30V. This would seem like a cold solder joint, but I've reflown every pin on the regulator, and every component besides it (the ferrite and the three capacitors, who give stability to the chip if I'm not wrong). I've even changed the regulator for another one, because I thought the first one was dead on arrival or killed by heat or something. But no.

 

What could it be? Pictures in the gallery.

 

http://imgur.com/a/KfUkh

 

EDIT: also removed the ferrite between the reg and the other ICs to check if there was a short somewhere along that way, and nothing. The circuit seems okay, it's jut the region of the regulator.


Edited by patchoncas - 8/1/14 at 8:46am
post #1068 of 1073

Is there 5 volts at the input to U2?

If there is, remove C7, C8 and L3.

Is there a short under C7 or C8.

Is there 3v3 from U2 now?

If no, replace U2.

Is it working now?

If yes, re-install C7, C8 and L3
 

post #1069 of 1073

1. Yes

2. No shorts

3. No, but I reflowed it (yet again) and now it gives me an oscillating value, between 2.8 and 3.4. Looking good.

4. Soldered the caps: voltage drops to 0.5 or so again. What the hell? I guess I have bad caps.

 

Is it possible that I have received a bad batch of regulators?


Edited by patchoncas - 8/1/14 at 12:07pm
post #1070 of 1073

Which cap causes it to stop working?

post #1071 of 1073

C8 is the noise reduction cap for the regulators internal reference.

C7 is an input bypass cap in parallel with the electrolytic on the

other side of the board.

 

If either of these were to cause a problem, it would be C8.

 

What about C14...it is directly on the output of the regulator.

Have you removed and checked it?

post #1072 of 1073

Thanks for the support, Avro!  I've been awfully busy lately and unable to check on things as often as I should.

post #1073 of 1073
Quote:
Originally Posted by juswyq View Post
 

I am confused about this issue though - I read the documents for the "C" revision of the PCM2706/7 and it seems like they only changed the behaviour of the volume control (i.e. how the volume changes with the win7 volume slider); the "C" variant doesn't seem to enable the volume control. 

 

The document is here: http://www.ti.com/lit/an/sbfa019/sbfa019.pdf

 

I'm trying to isolate the problem: is my non-functioning master volume control due to me using PCM2707 instead of PCM2706, or is it because I'm using the non-C revision?

 

Desoldering and resoldering the IC chip will be a nasty job...

 

Quote:
Originally Posted by tomb View Post

I can't guarantee anything, but this has been a long standing issue with Win7. There is no difference with respect to 2707 or 2706 for this issue. The 'C' variant is supposed to address it.

As stated however, I can't guarantee anything about your personal setup. I just thought that maybe you could confirm it for all of us.

If you're afraid to mess with it, I can certainly understand.

 

Tragedy! I tried to desolder the PCM2707 chip and but burnt some solder pads off the board. Now the board is useless and I have wasted the other parts that are already soldered on :(

 

I then built a Pupdac with a PCM2707C after much effort (the pcm1794 is a tough job). Alas, the volume control in windows 7 is still not working.

 

I am now contemplating whether to order another grubdac and pupdac board to do a better job.

 

Thank you for your help Tom!

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