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Alien DAC v1.1 Construction Thread - Page 85

post #1261 of 1560
6/11/08 at 1:55am
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.
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post #1262 of 1560
6/11/08 at 11:43am
Quote:
Originally Posted by CingKrab View Post
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.
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post #1263 of 1560
6/11/08 at 9:33pm
disregard this
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post #1264 of 1560
6/24/08 at 1:19pm
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
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post #1265 of 1560
6/24/08 at 1:51pm
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.
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post #1266 of 1560
6/24/08 at 3:10pm
Quote:
Originally Posted by ruZZ.il View Post
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.
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post #1267 of 1560
6/24/08 at 3:22pm
Quote:
Originally Posted by tomb View Post
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.
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post #1268 of 1560
6/24/08 at 5:01pm
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!
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post #1269 of 1560
6/24/08 at 5:37pm
Quote:
Originally Posted by ruZZ.il View Post
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?
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post #1270 of 1560
6/24/08 at 6:15pm
Quote:
Originally Posted by Colonel Panic View Post
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..
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post #1271 of 1560
6/24/08 at 11:17pm
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.
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post #1272 of 1560
6/25/08 at 3:35am
is in in the top right corner? if so check the schematic, two pins are shorted anyway.
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post #1273 of 1560
6/25/08 at 11:04am
Quote:
Originally Posted by Colonel Panic View Post
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.
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post #1274 of 1560
6/26/08 at 1:24am
Quote:
Originally Posted by Pars View Post
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!!
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post #1275 of 1560
6/26/08 at 1:49am
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.
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