1708 - U3 shorted while antenna plugged in

[Massimo1993]

Hi, sorry but i can't seem to figure out what is the problem.
The u3 chip is shorted when the wifi antenna is plugged in. Detaching the antenna removes the short.
Another user did have the same problem but didn't post a solution and didn't answer to me yet.
Hope someone can help me figure this out, it seem it's a common problem.

[RDC]

I can't see how that's even remotely possible, unless the connector is bent and the shielding of it is hitting something on the board when you're plugging it in. If it's plugged in and pointed left there's nothing for it to hit. If it's pointed left and up a bit, it can hit the left side of C52 which would cause the 3.3v rail to short to ground, and U3 provides that 3.3v rail.

[Massimo1993]

I can't see how that's even remotely possible, unless the connector is bent and the shielding of it is hitting something on the board when you're plugging it in. If it's plugged in and pointed left there's nothing for it to hit. If it's pointed left and up a bit, it can hit the left side of C52 which would cause the 3.3v rail to short to ground, and U3 provides that 3.3v rail.

Thanks for the reply. Unfortunately the shielding didn't hit anything i've checked.
I did remove the u3 hoping that was the problem but the output of the u3 when the antenna it's plugged in it's shorted to ground.


the second left pin starting from top.
https://www.acidmods.com/RDC/XB1/1708%20TBT.jpg

[RDC]

You can try desoldering the antenna (on the button/power board side) and unplug it, see if it's shorted internally. If it's not, then leave it desoldered and see if the short is there when it's plugged in.

Unless that MCU is beyond fragged, or there's some solder splash in some really wierdo place, I still can't see how that's causing a short on the 3.3v rail when plugged in.

Are we talking dead short, like 0 ohms? or a few ohms of short when it's plugged in?

Does anything else get warm besides U3? You can hit the board with some rubbing alcohol here and there and see if it evaporates quicker from any components.

[Massimo1993]

You can try desoldering the antenna (on the button/power board side) and unplug it, see if it's shorted internally. If it's not, then leave it desoldered and see if the short is there when it's plugged in.

Unless that MCU is beyond fragged, or there's some solder splash in some really wierdo place, I still can't see how that's causing a short on the 3.3v rail when plugged in.

Are we talking dead short, like 0 ohms? or a few ohms of short when it's plugged in?

Does anything else get warm besides U3? You can hit the board with some rubbing alcohol here and there and see if it evaporates quicker from any components.

The antenna itself isn't shorted but the antenna ground pad has continuity with the antenna core pad (not sure it's the correct name) and i doubt this is a normal thing.



The U3 short it's 1.4ohm when plugged in and it's the only components that gets incredibly hot.
Btw the short it's present even with just the antenna connected, without connecting the 2 boards directly.

[RDC]

That's perfectly normal because of how the antenna works. The center lead goes thru a filter network to ground, Z1, Z2 and Z3, so measuring it from ground to the center lead will measure a direct short Ohm wise.

Does that controller work otherwise with the antenna unplugged? I wouldn't expect it to work wireless, but does everything else function normally over the USB connection?

Without the boards connected, the 3.3v rail is nowhere near that antenna line, so that makes even less sense now.