Last night I was swapping out the servo clip for a Crossfire Nano RX on my brand new GepRC Crocodile Baby PNP and messed up the soldering wile de-soldering the servo harness. I had some bridging and stuff, so it took me a while to get that cleaned up using flux and a wick. I was trying hard not to solder too long and remove a pad, I've done that before! Eventually I got the new Nano Rx installed, but had trouble with getting input to show up in Betaflight. I eventually noticed there was some tiny bits of solder probably bridging, so I used an Xacto blade to remove those little solder strands, then used alcohol wipes to clean up any left over flux or anything.

As far as I knew, everything was ready to go last night, but I may have not tested video after I cleaned up the Nano soldering, can't remember for sure. Anyway, this morning I put some shrink wrap on the RX and put the rest of the quad back together. When I tried to get ready to fly, I didn't have video, just a black screen, no OSD. I think I had just changed the OSD from Auto to NTSC before I looked in the goggles. I've had that make my video go black before, so I tried all 3 options with disconnecting, unplugging and powering up again. Still just black. I can see in my Rapidfire 2 OSD that it's putting a signal out on the channel I'm tuned to.

I tried plugging in a spare brand new camera, nothing changed.

I wired the yellow wire from the camera to the yellow wire on the VTX and nothing changed.

I verified with a multimeter that the camera is getting power.

I never had the VTX on without the antenna attached.

The things I'm wondering are:
Maybe I had the VTX on for too long last night while plugged into USB and something burned out?
Is it still a PAL/NTSC issue that somehow a reboot hasnt fixed?
When I was cleaning up the Nano soldering with an Xacto blade, did I accidentally cut some circuitry?

I don't know what else to do other than try another VTX, but I feel like my soldering has gotten worse and there are a lot of tiny pads to de-solder, so I'm trying to put that off if possible. Plus, based on lots of googling, it seems that if I have a black screen and no OSD, it's likely an issue between FC and VTX?

Dump All attached. The FC manual is here, but it doesn't show my exact VTX. It came with a similar one to the Tramp one they show. It came with a "STABLE 5.8G 600mW" with GepRC's name on the board. I can't find a pinout for it. This also came with the Caddx Ratel (v2 I think).

What's interesting, is that the camera connects to a plug on the VTX. I guess the camera is wired to the VTX and then the VTX sends the camera signal to the FC and then comes back with OSD, etc. in a bigger harness. Not that it matters, but in my limited experience, the camera is usually wired right to the FC.

Thanks in advance!

can you provide a foto of the wiring?
seems a try with another vtx is a good route.

I already started dismantling the wiring to try another VTX. I got the same result, a black screen, no OSD. So now I wonder if I should try the video from the camera directly to this other VTX? Or maybe I fried this VTX and didn't realize it a while ago. 

Here is a pic of it as it's currently wired to the TBS Unify Pro 32 5G. I temporarily spliced/soldered some of the wires together to do this test, I wouldn't plan on leaving it like that for flight.

Ugh this is so frustrating. I've taken a brand new quad and made it potentially unusable... I haven't even been able to fly it.

A black screen means the VTX is working and is transmitting a signal. If it wasn't you would just get snow / static.

The black screen with no OSD is a symptom that the OSC chip on the FC has a short on one of the legs or has gone bad. Use a magnifying glass to carefully inspect that 28-pin chip in the middle of the FC. That is the AT7456E OSD chip. Make sure there are no tiny solder balls or splatters of solder bridging any of the legs on it.

Ok I used a macro lens to get some close ups of a few areas:

Here's the OSD chip, not sure I see anything?



Here's another chip that might have some flux or goopy stuff briding from a pin to a pad in the lower right?



And here's where I did a bunch of poor soldering and then some cleanup for installing the Rx.

Is this a bit of fluff across these two pins or is it a minuscule strand of wire?

That's just fluff... I just removed it and tested again. No change.

You likely have a bad OSD chip then unfortunately. Check to see if you are getting a voltage to that chip on each of the 4 power pins. Details of that are in the following post...

https://intofpv.com/t-getting-a-signal-f...#pid128435

What I can't figure out is why when I sent video directly from the camera to the VTX it was still black. Should I try that again with this other VTX?

Sorry, I missed that vital bit of information. That suggests an issue with the camera but if that was the case then you would still expect to see the Betaflight OSD on the black screen. I'm not sure what goggles you have but if they are ones that take a module or have an analogue AV input option you can do a test the camera off the quad. See the post below.

https://intofpv.com/t-camera-tester-with...rk-goggles

This is the size of the tip of my multimeter, about 1cm above the board in this photo. I'm worried I could short something out on a neighboring pin while testing for voltage. Any tips? (no pun intended)


On that diagram you linked, for orientation, is the + symbol the same corner as the shiny circle I see on the top of my chip?

Should I get ground from anywhere on the board while testing?

Many thanks!

i would give it a try by switch the signal wire between vtx and video out of the flightcontroller, just to get sure its no broken wire.
if no luck wire the signal wire of cam and vtx together. you would be sure the vtx is working properly this way.


you can add a tape to the tip of the multimeter, to get a very small surface and it would need some force to get connection.

(26-Mar-2021, 08:06 PM)hugnosed_bat Wrote: i would give it a try by switch the signal wire between vtx and video out of the flightcontroller, just to get sure its no broken wire.
if no luck wire the signal wire of cam and vtx together. you would be sure the vtx is working properly this way.

Ok I will try this tonight. Do you mean switch the wires on the VTX pads?

When you say to then try wire cam and vtx together, do you mean yellow wire from camera to Video pad on VTX? Like wiring it directly?

Sorry, still pretty new to all this.

Ok some progress, I wired the cam video to the VTX directly and got the camera feed!

Then I switched the pads on the FC and just get video, no OSD. So I checked the FC pinout and that is actually correct. I had wired the VIN/VOUT backwards.

Then I hooked up Betaflight, and switched to PAL, rebooted and Video and OSD were back!

I still don't understand why the original VTX didn't work, because that was wired correctly from the factory. I bet I had a bit of something shorting out somewhere and didn't realize it was fixed from the various cleanings I've done because my "other" VTX was wired wrong.

Anyway, I'm elated! I think I'll try hooking the old VTX up since it's a bit more powerful and has a longer antenna, etc. But THANK YOU to all who helped me troubleshoot! This forum is priceless, you have no idea how happy I am!!!!!

So I tried hooking up the old VTX, but it still just gives a black screen. I can see that it is broadcasting on the desired channel based on the signal strength I see in my goggles OSD. I tested the camera by wiring it to the google module port, it still works. I tried wiring the camera directly to the VTX video pad, but I still just black screen.

Is it possible that a VTX can be bad (something fried in the video circuit) but still be broadcasting a signal?