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pupDAC Step-by-Step Build Thread - Page 10

post #136 of 348
Quote:
Originally Posted by tomb View Post
 

Well, for the Right channel - the 3rd and 4th pins from the bottom-right of the DAC chip are the Right channel outputs (IORN and IORP).  I don't see anything wrong with those pins, but there does seem to be a "whisker" bridge starting from the 5th pin up from bottom right.  I don't know if that's really something and whether it would have an effect on just the right channel, but maybe.

 

You've done an excellent job of soldering, especially on the two big chips.  It's a reflective-photographic effect, I think, but it almost looks like some of the opamp pins are dissolved. ;)  I would not suspect the opamp at first guess, though, since it's fairly easy to solder compared to the rest of the PCB.

 

See if you can clear that whisker on the DAC chip and them perhaps apply a bit more heat with a few strokes of the iron on those bottom 3rd and 4th pins.

Thanks. It was my second SMD soldering kit.. the first one i did 2 weeks ago was the gamma 1/2 which suffered from a hair of a Q-Tip...

 

But the whisker at the DAC was doing nothing. After reapplying a little bit of solder to all of the DAC pins, the right channel stillt outputs nothing :(

post #137 of 348
Thread Starter 
Quote:
Originally Posted by nini_knoxville View Post
 
Quote:
Originally Posted by tomb View Post
 

Well, for the Right channel - the 3rd and 4th pins from the bottom-right of the DAC chip are the Right channel outputs (IORN and IORP).  I don't see anything wrong with those pins, but there does seem to be a "whisker" bridge starting from the 5th pin up from bottom right.  I don't know if that's really something and whether it would have an effect on just the right channel, but maybe.

 

You've done an excellent job of soldering, especially on the two big chips.  It's a reflective-photographic effect, I think, but it almost looks like some of the opamp pins are dissolved. ;)  I would not suspect the opamp at first guess, though, since it's fairly easy to solder compared to the rest of the PCB.

 

See if you can clear that whisker on the DAC chip and them perhaps apply a bit more heat with a few strokes of the iron on those bottom 3rd and 4th pins.

Thanks. It was my second SMD soldering kit.. the first one i did 2 weeks ago was the gamma 1/2 which suffered from a hair of a Q-Tip...

 

But the whisker at the DAC was doing nothing. After reapplying a little bit of solder to all of the DAC pins, the right channel stillt outputs nothing :(

OK - I'll keep looking at the pics.

post #138 of 348
Quote:
Originally Posted by tomb View Post
 

OK - I'll keep looking at the pics.

Thank you very much. I really don't know how to troubleshoot it any further without ruining my board or removing those chips, which will be a pain in the a**.

post #139 of 348
Thread Starter 

Just a gut check, but can you check the R21 resistor?  In your PCB-bottom pic, it's the far right blue resistor beneath the opamp.  Check to confirm continuity on both ends and see if registers 10 ohms.

post #140 of 348
Quote:
Originally Posted by tomb View Post
 

OK - I'll keep looking at the pics.


I had a look too...I didn't see anything either

post #141 of 348
Quote:
Originally Posted by tomb View Post
 

Just a gut check, but can you check the R21 resistor?  In your PCB-bottom pic, it's the far right blue resistor beneath the opamp.  Check to confirm continuity on both ends and see if registers 10 ohms.

10.1 ohms...

post #142 of 348
Thread Starter 
Quote:
Originally Posted by nini_knoxville View Post
 
Quote:
Originally Posted by tomb View Post
 

Just a gut check, but can you check the R21 resistor?  In your PCB-bottom pic, it's the far right blue resistor beneath the opamp.  Check to confirm continuity on both ends and see if registers 10 ohms.

10.1 ohms...

Dang!  I'll keep looking.  I see no reason to even consider removing the big chips, though - the joints look great from here (assuming that whisker was nothing).  Maybe something else will pop out at us.

post #143 of 348

What are the voltages around the op amp?

There should be at least a little offset or

voltage on every pin.

post #144 of 348

 

I have 118mV offset on the op amp inputs.

And something like 5mV on one output

and 16 mV on the other.

post #145 of 348
Thread Starter 
Quote:
Originally Posted by Avro_Arrow View Post
 

 

I have 118mV offset on the op amp inputs.

 

And something like 5mV on one output

and 16 mV on the other.

Knoxville - you never told us the actual values you got from measuring the opamp inputs.  Is it close to what Avro is quoting?

post #146 of 348
Quote:
Originally Posted by tomb View Post
 

Knoxville - you never told us the actual values you got from measuring the opamp inputs.  Is it close to what Avro is quoting?

It's running pretty late here in germany now, i will measure those tomorrow after work and let you guys know.

post #147 of 348

I hope my measurments are okay (i'm not used to measure opamps...)

pin1 & pin2: 92mV

pin1 & pin3: 123mV

 

but for the output:

pin7 & pin5: 1.1V

pin7 & pin6: 2.1V

 

So what does this mean? The input offset is somewhere in avro's range, but the output is like through the roof

post #148 of 348
Thread Starter 
Quote:
Originally Posted by nini_knoxville View Post
 

I hope my measurments are okay (i'm not used to measure opamps...)

pin1 & pin2: 92mV

pin1 & pin3: 123mV

 

but for the output:

pin7 & pin5: 1.1V

pin7 & pin6: 2.1V

 

So what does this mean? The input offset is somewhere in avro's range, but the output is like through the roof

Yep, you're right.  Let me look at the schematic and your pics some more and see if I can figure it out.  When you get a chance, you might take a close look at the through-hole resistors and see if maybe you got some mixed up.

post #149 of 348
Thread Starter 

Here are some suggestions:

 

It's hard to tell - your photos are great - but some of the solder joints may be cold.  In particular, it appears that some of the resistor leads look like they've been poked through the solder.  I'm sure that's not the case, only that it's some indication the joint may be cold.  So, be methodical about it, but start with the through hole resistors and see if you can re-flow the solder on their joints.  For instance, R14 and R15 take the Right channel outputs from the DAC chip directly.  If there's something faulty in the connection there, that may explain the lack of audio output in the right channel.  Go through all the resistors this way, stop, then re-measure with the power off and check for good continuity throughout the circuit.  A way to do this is - with power off - touch one DMM probe to the output pin on the DAC chip, then touch the other probe to the far lead (toward the opamp) of the resistor.  If you can read zero ohms, then things are OK.  Do this for the C3 and C18 mica capacitors, too.  While you're at it - also check L5.  One of the capacitors is blocking it, but it looks a bit dodgy on the right side.

 

Let us know what you find when you have a chance. :)

post #150 of 348
Quote:
Originally Posted by nini_knoxville View Post
 

I hope my measurments are okay (i'm not used to measure opamps...)

pin1 & pin2: 92mV

pin1 & pin3: 123mV

 

but for the output:

pin7 & pin5: 1.1V

pin7 & pin6: 2.1V

 

So what does this mean? The input offset is somewhere in avro's range, but the output is like through the roof


My voltages are referenced to Gnd (at the RCA), not from one pin to another.

On the + and - inputs, there was only a couple mV difference in the four pins.

The lowest was 117mV and the high was 119mV. And of course, the +2.5 and

-2.5 supply voltages. The output offset should be less than 10mV but a little

higher is not uncommon in the pupDAC.

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