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Comments for my PCM2702 DAC layout? - Page 40

post #586 of 613
10/3/09 at 11:46pm
There may have been a bridge between L3 and the USB connector, can't be sure now as I have removed L3, L4, C8 and the USB connector from the board. That area of the board is so tightly packed it was hard to see so I decided to clear it and redo all those parts again.

Replacement parts on the way.
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post #587 of 613
10/12/09 at 2:43am
So I've finally gotten some time to work on my non-functioning Bantam. When I plug it in, it is unrecognized by the computer and IC2 (4.75V) heats up immediately. I haven't had a chance to check the voltage coming out of it since I disconnected it so quickly to prevent damage. Any idea what's causing this? I'll get some pics up tomorrow but was hoping someone had run into this before.
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post #588 of 613
10/12/09 at 7:47am
Quote:
Originally Posted by Juaquin View Post
So I've finally gotten some time to work on my non-functioning Bantam. When I plug it in, it is unrecognized by the computer and IC2 (4.75V) heats up immediately. I haven't had a chance to check the voltage coming out of it since I disconnected it so quickly to prevent damage. Any idea what's causing this? I'll get some pics up tomorrow but was hoping someone had run into this before.
Nope - haven't heard of it, as far as I can remember. However, it sounds like a part is out of place or something is bridged. Hopefully, someone can spot the trouble from your forthcoming pics.
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post #589 of 613
10/13/09 at 3:44pm
Well I figured it out. If you take a high-powered flashlight (CREE-LED or similar) and shine it through the PCB, you can see the legs on the PCM2702 and easily see tiny bridges. I found one between two pins around pin 18 or so that I hadn't on visual inspection. I believe it was shorting the 4.75V to GND, hence the heating and non-functioning.

I've repaired the bridge and no longer have heating, but the voltage across C13 (i think it's C13, it's the 4.75V cap) is 5V, so I think I've blown the TPS reg. I'm wondering if exposing all the 4.75V pins to 5V may have fried the DAC; if so, I'd rather start from scratch with a new DAC than replace the TPS and still not have it work.
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post #590 of 613
10/13/09 at 3:49pm
The 4.75 pin are designed for 5V and have an absolute max tolerance of 6.5V per the datasheet.
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post #591 of 613
10/13/09 at 4:23pm
Quote:
Well I figured it out. If you take a high-powered flashlight (CREE-LED or similar) and shine it through the PCB, you can see the legs on the PCM2702 and easily see tiny bridges.
That is by far the best method when it works! Saved me twice so far.
Anyway good luck I hope it works when you replace the reg.
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post #592 of 613
10/13/09 at 5:21pm
Quote:
Originally Posted by cobaltmute View Post
The 4.75 pin are designed for 5V and have an absolute max tolerance of 6.5V per the datasheet.
Awesome; I was looking through the datasheet but must have missed it. Here's hoping replacing the reg works!
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post #593 of 613
10/13/09 at 5:50pm
Quote:
Originally Posted by Juaquin View Post
Awesome; I was looking through the datasheet but must have missed it. Here's hoping replacing the reg works!
If I'm reading the datasheet correctly on the reg, the min and max on the TPS793475 output is 4.655VDC and 4.845VDC, respectively, when fed with a voltage between 5.25V to 5.5V. I'd say it's blown. After all, you had it connected to a dead short with that bridge. Not many IC's/transistors can survive that for long. Sorry.
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post #594 of 613
10/13/09 at 7:01pm
My comment was for the PCM2702, and was in response to this:

Quote:
Originally Posted by Juaquin View Post
I'm wondering if exposing all the 4.75V pins to 5V may have fried the DAC; if so, I'd rather start from scratch with a new DAC than replace the TPS and still not have it work.
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post #595 of 613
10/13/09 at 7:08pm
Quote:
Originally Posted by cobaltmute View Post
My comment was for the PCM2702, and was in response to this:
Ah - I can read data sheets but not posts. Still, the TPS definitely sounds blown.

EDIT: Of course, you are correct about the PCM chip. After all, there were configuration options with the Alien DAC that used no regulation at all - just straight from the USB power.
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post #596 of 613
10/13/09 at 7:11pm
Yeah, I'm only wondering about the health of the PCM - I know the reg is blown to bits. Poor thing was trying to make ground equal 4.75V, and it lost

However, in theory, even if the TPS is blown and supplying 5V, shouldn't the PCM still work (considering the comment about the Alien running without regulation)? Or is there something that actually requires 4.75V and is not 5V-tolerant?
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post #597 of 613
10/13/09 at 7:25pm
Quote:
Originally Posted by Juaquin View Post
Yeah, I'm only wondering about the health of the PCM - I know the reg is blown to bits. Poor thing was trying to make ground equal 4.75V, and it lost

However, in theory, even if the TPS is blown and supplying 5V, shouldn't the PCM still work (considering the comment about the Alien running without regulation)? Or is there something that actually requires 4.75V and is not 5V-tolerant?
Yes (it should've worked), assuming you cleared those bridges and there wasn't any damage.
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post #598 of 613
10/13/09 at 7:48pm
Hmm. May just need to start over then, probably fried the DAC. Thanks for the help guys!
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post #599 of 613
10/24/09 at 4:51pm
Hi all,

Yet another troubleshooting post. My computer is not recognizing the dac, so I guess there is a problem with IC1 or the chip (or both).

I'm reading 2.10V across C11 and IC1 looks like it could use some more solder, but I have a pretty cumbersome iron and wanted to consult the experts before I start soldering again . Is there a particular pin I should be focusing on? Thanks!

edit: Unfortunately, I don't have a camera with me right now.
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post #600 of 613
10/24/09 at 5:21pm
Quote:
Originally Posted by Dan55 View Post
Hi all,

Yet another troubleshooting post. My computer is not recognizing the dac, so I guess there is a problem with IC1 or the chip (or both).

I'm reading 2.10V across C11 and IC1 looks like it could use some more solder, but I have a pretty cumbersome iron and wanted to consult the experts before I start soldering again . Is there a particular pin I should be focusing on? Thanks!

edit: Unfortunately, I don't have a camera with me right now.
Sounds like you know where to look. IC1 should be producing 3.3V across C11. I can't tell you what pin to focus on, but a pic or two may help if you don't solve it.
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