I need help identifying a component on the Xbee 5v/3v adapter board Rev B

ElectricAye

Thanks to my poor soldering skills, I managed to create a solder bridge while soldering the long headers to the Xbee 5v/3v adapter board Rev B.
While fixing the solder bridge, I managed to pop loose a teeny tiny component that sets between the SLP and VREF pins. It's rectangular, somewhat yellowish, and too small for me to solder back onto the board, so I'm hoping I can either live without it or attach a replacement component external to the board. Problem is, I can't match it with the schematic, so I'm clueless as to what it is. I've attached a photo with the component circled. I hope somebody here can tell me what it is.

Many thanks.

ElectricAye

I tried to measure the resistance of the little speck but could not get an ohm reading, so I suspect it might be a capacitor.
One end of it appears to be tied to a ground plane, so I'm now suspecting it's the C2 capacitor (0.1 uF) seen in the following RevB schematic:

http://www.parallax.com/Portals/0/Downloads/docs/prod/rf/32401-XBee5V_3.3VAdapter_BSchematic.pdf

But that's just a guess at this point. I suppose if it's the C2, then I could place a 0.1 uF cap across Vcc and GND as an external connection.

Anybody know for sure?

Leon

Use a DVM to check continuity to the parts around it, that should show you which component it is.

ElectricAye

Leon wrote: »

Use a DVM to check continuity to the parts around it, that should show you which component it is.

Thanks, Leon, but doesn't a small capacitor such as 0.1 uF look like an open circuit to a simple DVM? or are there DVMs that have some kind of capacitor tester thingy?

Leon

I meant check the continuity of the ends or the pads to other parts, to see what they are connected to. The fact that it is a capacitor is irrelevant.

Phil Pilgrim (PhiPi)

ElectricAye wrote:

But that's just a guess at this point. I suppose if it's the C2, then I could place a 0.1 uF cap across Vcc and GND as an external connection.

That would be C2. For correct performance, you should try to solder it back in place. Just connecting a through-hole cap between Vdd and Gnd will not supply the same bypass performance due to lead inductance. Also, without knowing what kind of cap C3 is, the regulator might not be stable without C2 in place where it belongs.

That said, you might be able to get by with just leaving it off the board. But, if you do, check Vdd with both a scope and voltmeter to make sure it's 3.3V and not oscillating.

-Phil

ElectricAye

Phil Pilgrim (PhiPi) wrote: »

That would be C2. For correct performance, you should try to solder it back in place. Just connecting a through-hole cap between Vdd and Gnd will not supply the same bypass performance due to lead inductance. Also, without knowing what kind of cap C3 is, the regulator might not be stable without C2 in place where it belongs.

That said, you might be able to get by with just leaving it off the board. But, if you do, check Vdd with both a scope and voltmeter to make sure it's 3.3V and not oscillating.

-Phil

Thanks, Phil. I'll try leaving it off the board and see what happens. There's no way I personally could ever get that little booger of a component back into its position. I'm terrible when it comes to these tiny things.

Thanks again.

ElectricAye

Leon and Phil,

thanks for your help. I got it working tonight and all seems well.