[Bismar]

 

[amb]

Check for cold joints on U3U, in particular pin 2 (the middle one on the side with 3). It should be connected to ground. You can use the ground strips along the edges of the board for your DMM.

 

[GeWa]

My boards + stuff and custom plates arrived today. Thanks Ti

Regards

 

[Bismar]

I reflowed U2U and U3U still ~4.5 volts on the 3.3v test point.

Is it possible i may have damaged one of the SMD's? And if so, how do i test if they are dead?

Also the computer does not recognize the usb board if that helps.

 

[amb]

Quote:

Originally Posted by Bismar /img/forum/go_quote.gif I reflowed U2U and U3U still ~4.5 volts on the 3.3v test point. Is it possible i may have damaged one of the SMD's? And if so, how do i test if they are dead?

Well, before you gebugging anything else, the supply voltage has to be right first. That leaves only the voltage regulator chips themselves. Did you use the wrong chip for U3U? What does its markings say?

 

[MisterX]

Ti....from this image --->
http://img120.imageshack.us/img120/4233/1001822zv9.jpg

U3U = "LORA" (LP2985AIM5-3.3)

But I cannot tell from the pics what the numbers are on U2U so....

 

[amb]

Ok, so it's the correct chip. Aside from bad solder joints there is not much else that could cause the voltage to be incorrect, unless the regulator itself is blown (as an internal short).

 

[Bismar]

U2U reads A08G.
U3U reads LORA.

I don't have spares of either of those, only have a spare PCM2707 but that's hard to remove and i wouldn't want to unless you guys are really sure.

I already tried reflowing the joints, so i don't think its a bad solder joint. Is there anything else i can test ? Maybe some other component thats linked to either of those chips under power?

 

[amb]

Nothing will cause the voltage regulator to output more voltage than what it's supposed to output, unless its ground reference pin is not making contact to circuit ground, or there is a short circuit from its input to output (which could be an internal short due to a blown regulator, or a solder bridge somewhere, or a PCB defect). You said that you/ve reflowed the regulator's joints, so you've probably eliminated the first possibility. That leaves the others. Have you measured the resistance between pins 1 and 5 of the voltage regulator chip?

 

[Bismar]

Quote:

Originally Posted by amb /img/forum/go_quote.gif Nothing will cause the voltage regulator to output more voltage than what it's supposed to output, unless its ground reference pin is not making contact to circuit ground, or there is a short circuit from its input to output (which could be an internal short due to a blown regulator, or a solder bridge somewhere, or a PCB defect). You said that you/ve reflowed the regulator's joints, so you've probably eliminated the first possibility. That leaves the others. Have you measured the resistance between pins 1 and 5 of the voltage regulator chip?

Pin 1-5 = 1339 ohms
Pin 2- Ground strips = 0 ohms

 

[Bismar]

Come to think of it, Pin 1-5 should be way more ohms then that, seeing its off unless the multimeter somehow made the logic go high.

Ok maybe not, the U5D chip on the other board shows 1160 ohms.

In fact most of its resistance to ground is similar to the one on the USB board.

 

[amb]

I would try removing U3U and see if the short persists on the board, or if it's within the chip.

 

[Bismar]

Quote:

Originally Posted by amb /img/forum/go_quote.gif I would try removing U3U and see if the short persists on the board, or if it's within the chip.

So, if i remove it from the board i should expect 0 volts at 3.3v test point? How about the 5v test point?

And if i still get a voltage at the 3.3v test point then it's a short from somewhere else?

 

[amb]

That's correct, without U3U there shouldn't be any voltage at the 3.3V test point. The 5V test points should still be about 5V when it's plugged into the USB port. Obviously, without a 3.3V to supply the chips the computer won't detect anything.

If you still get more than a couple volts at the 3.3V test point without U3D, then there is a short somewhere on the board.

 

[Bismar]

Hahahah.

This is gold, somehow by measuring each of the pins resistance to ground, i have made it to work.

Pretty much decided to test it one last time before i proceeded to desolder it and it WORKS!!!

Thanks for all your help amb and MisterX.

Windows detects it, and i am now playing some music through it