I ripped the u.fl connector pad off of my VTX in a crash.  Bought a spare and tried to solder it in place but am not convinced the connections are good.

With the VTX removed I can attach a battery and fly LOS without issue.

With the VTX installed when I plug in a battery I get the first three tones from the ESCs, but then no more.  What could be the issue here?

You might have a short on the VTX which is affecting the power circuit of the FC. That would be my first guess. Maybe you caused a short when you soldered on the U.FL connector, or accidentally damaged something.

Disconnect the VTX and then check for any short circuits on the power rails of the VTX itself.

(22-Aug-2020, 04:08 PM)SnowLeopardFPV Wrote: You might have a short on the VTX which is affecting the power circuit of the FC. That would be my first guess. Maybe you caused a short when you soldered on the U.FL connector, or accidentally damaged something.

Disconnect the VTX and then check for any short circuits on the power rails of the VTX itself.

I'll have to ask you to please excuse my general noobiness.  Can you tell me what you mean by power rails?  The VTX connects to the FC via 10 pins on the underside (see attached images), I'm not sure how I'd go about testing these?

       

Below is the pinout for the VTX used on the GEPRC F411 Stable 16x16 stach that the Phantom uses. With the board removed from the stack, do a continuity test between each of the VCC_IN pins and GND pins on that pin header stack.

(22-Aug-2020, 09:37 PM)SnowLeopardFPV Wrote: Below is the pinout for the VTX used on the GEPRC F411 Stable 16x16 stach that the Phantom uses. With the board removed from the stack, do a continuity test between each of the VCC_IN pins and GND pins on that pin header stack.

OK, it appears that I have continuity between both VCC_IN pins and all of the GNDs. So I think we've just confirmed that my soldering job was crap, right?  And probably my options are to try to redo the soldering job (that stuff is so small!), or just get a replacement VTX.

Can you help me to understand what is happening when I power the quad with the VTX attached?  I think the first three rising tones from the ESC, which I am getting, just indicate power up.  And the second two, which I am not getting, are beginning and end of the arming sequence (throttle signal detected / zero throttle detected).  I don't know why a short in the VTX would disrupt the arming.  Does the short in the VTX essentially carry through to the FC?

The short in the VTX will effectively cause a short on the 5V power rail on the FC when the VTX is connected to the FC. The 5V power rail supplies the 3.3V regulator which in turn powers the MCU. If the MCU isn't being powered then there will be no signal from the MCU to the ESCs, which is why you won't be getting the last two beeps. Those last two beeps indicate a valid throttle signal from the MCU.