[Colonel Panic]

Repeat after me:

I will NOT sneeze while placing positioning C14.

The behind of my desk is a black abyss where nothing returns from. I searched and searched but C14 was nowhere to be found.

 

[Pars]

Quote:

Originally Posted by CingKrab /img/forum/go_quote.gif Just checked VCCL, AGNDL, and OUTL. All ~0 ohms (0.1 according to my meter) from top of the pin to the pad. VCCL is around 4.71V at the pin. AGNDL is connected to both the USB receptacle shield and OG according to the continuity test at the pin. I'll try reflowing some stuff related to those pins, but it looks like the left channel analog stuff is properly powered at least. I'll try reflowing R15 again.

The only other thing I would do is with DMM check adjacent pins for shorts. Note that some of the end pins on one side of the PCM are intentionally shorted on the PCB (right lower side of chip, forget pin #s). You might also check OUTL to ground compared to OUTR to ground, etc. Large differences should point to a problem.

I rebuilt one user's Alien, moving all parts to a new board, and after that abuse, the PCM still worked, so I'm not sure I'd give up on it just yet.

 

[TimmyMac]

disregard this

 

[ruZZ.il]

Hey fellas, I seek any suggestions, or confirmation of a dead chip ;(
This DAC was functional for quiet some time, and still partially is:
Sound out of only a single channel (The right one).
I've scoped out the actual chip pin, OUTL, and only get a slight offset, but no signal at all. OUTR is fully functional, so its not a power problem, no data transfer problem.. in fact, other than a single cap and resistor in the way, there's nothing but a faulty chip if 1 channel works perfectly and the other has no signal, or am I missing something? Balance and all other settings are set right, so.. changing chips? or.. any suggestions?
As always, much appreciated

Thanks

-R

 

[bhjazz]

Weird. You mentioned that all other settings are right. Did you check the 3.3v and 5V test points? Perhaps one of the resistors between the usb power in and the chip has gone. I know the right channel is working...I'll have to take a look at the schematic.

 

[tomb]

Quote:

Originally Posted by ruZZ.il /img/forum/go_quote.gif Hey fellas, I seek any suggestions, or confirmation of a dead chip ;( This DAC was functional for quiet some time, and still partially is: Sound out of only a single channel (The right one). I've scoped out the actual chip pin, OUTL, and only get a slight offset, but no signal at all. OUTR is fully functional, so its not a power problem, no data transfer problem.. in fact, other than a single cap and resistor in the way, there's nothing but a faulty chip if 1 channel works perfectly and the other has no signal, or am I missing something? Balance and all other settings are set right, so.. changing chips? or.. any suggestions? As always, much appreciated Thanks -R

It could be a pin that's pulled loose from being under tension over time. Check the chip's pins by placing a probe at the pin exit from the plastic shell. Put the other probe somewhere away from the immediate area, but still within the pad's conductive plane. Measure for zero ohm continuity and see if anything has changed. You might try something similar on the OL/OR caps and the resistors, too.

 

[bhjazz]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif It could be a pin that's pulled loose from being under tension over time.

Excellent idea. This could also come from the mechanical nature of the USB plug being connected and disconnected. I know my USB cable is quite snug and requires a bit of force, so any force there could turn or twist the board itself.

 

[ruZZ.il]

Tom, I did something similar. I used my old scope to find a signal between OUTL and ground. I used a resistor clipping as my probe, nada. The power supplies are all good, too, and the right channel works perfectly. Little else to blame here, I'm afraid

Thanks for the suggestions so far guys, I hope one helps!

 

[Colonel Panic]

Quote:

Originally Posted by ruZZ.il /img/forum/go_quote.gif Tom, I did something similar. I used my old scope to find a signal between OUTL and ground. I used a resistor clipping as my probe, nada. The power supplies are all good, too, and the right channel works perfectly. Little else to blame here, I'm afraid Thanks for the suggestions so far guys, I hope one helps!

I'm just a noob when it comes to DIY, but why not just reflow everything?

 

[ruZZ.il]

Quote:

Originally Posted by Colonel Panic /img/forum/go_quote.gif I'm just a noob when it comes to DIY, but why not just reflow everything?

If there were a signal at the chips output, then the prob would be between the chip and the board, I'd reflow the contact and check the rest of of sig. path. Since there's no measurable signal there, it doesnt seem to be a contact issue. Also, since I measure dc offset at the output, there's no true short to ground, so I'd assume that if it were creating a signal, it would be measurable. Also, since I can measure the offset, its not a problem with contact... I'll probably switch the chip out soon. fortunately, I have one around..

 

[Colonel Panic]

How easy is it to fry PCM 2702?

I missed a solder bridge between two pins before I plugged it in.

The computer recognized it, and it works according to the computer, but i'm getting short values from the two test pads.

 

[adamus]

is in in the top right corner? if so check the schematic, two pins are shorted anyway.

 

[Pars]

Quote:

Originally Posted by Colonel Panic /img/forum/go_quote.gif How easy is it to fry PCM 2702? I missed a solder bridge between two pins before I plugged it in. The computer recognized it, and it works according to the computer, but i'm getting short values from the two test pads.

When you say short values from the two test pads, do you mean the +5V and +3.3V test pads measure as shorts (0 ohms) to ground? Or which test points are you referring to? OL and OR? Check all the SMT caps, etc. as this is usually the area that a short occurs in.

 

[Colonel Panic]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif When you say short values from the two test pads, do you mean the +5V and +3.3V test pads measure as shorts (0 ohms) to ground? Or which test points are you referring to? OL and OR? Check all the SMT caps, etc. as this is usually the area that a short occurs in.

Sorry, I did in fact mean the +5V and +3.3V test pads to ground are giving me nothing near what they should.

Check the caps eh? this is going to be fun!!

 

[Pars]

Do you mean voltage measurement when you say the 5V and 3.3V aren't giving you near what they should? Do they measure as shorts (ohms)?

Looking at the schematic, there really isn't anything in common between the two regs that would pull both voltages down, unless the input voltage is way low, which feeds both. C21 or C31 shorted could do that. See what V+ measures or if it is shorted to ground with your meter.