Guten Tag my dear Pilots from overseas,

Since this is my first active thread i`d just take one sentence to indtroduce myself. I was already alot on this forum as guest when I needed answers or just follow discussions- so now i though this is the time to join sicne i didnt find anything like this before^^ Im Basti from Germany who just got into the hobby again. I was now going for the digital system, since the analog video feed is unbearable once you tried the digital one... 

Long story short I am using a Geprc MArk 4 HD 5" Frame with my dji air unit, a Mamba F405 stack - everyhting worked fine in the beginning.
After a face to face meeting with a tree my FC MCU chip got shorted and i had to replace the FC. Now when i wanted to try it out my custom osd wasnt showing inside the goggles anymore. I was checking everything i could find (enable custom osd in goggles, right uart RX/TX, enable OSD in betaflight, enable the MSP, etc...) 

I thought maybe setting the Air unit and goggles back to factory settings would help, but then i realized, that the USB connection is flicking on and off when i connect it to the PC.

Has anyone ever had something like this before? Does this mean my Airunit is somewhat fried?

Thanks in advance
 -Basti

When you say "flickering" connection, what do you mean exactly? Does the USB connection to the Air Unit repeatedly keep connecting and disconnecting from your computer?

I take it that you've tried another cable, and tried a different USB port on your computer? If you have then it's possible that the crash caused the USB socket in the Air Unit to get partially knocked off the circuit board so the contacts are no longer making permanent contact with the traces.

Hey, thank you for your response!

Yeah I already tried 2 different cables on two diffrent ports (one ubs-c to usb-c, the other ubs-c to usb 3.0)-the same behaviour on both cables and ports. As you said it keeps disconnecting and connecting, sometimes it stays in one state for half a minute, sometimes its switches multiple times per second.

Btw. the video connection is working fine.

Did you try it on another computer (assuming you have one)?

Good idea, but on my Laptop it has the same behaviour. I bought it used, so i dont have the bill for it in case its coverd by guarantee.
Im glad i updated everything 1 Month ago so i shouldnt run into firmware problems soon (hopefully)

I mean i can fly, but with no data of my Battery Voltage i always have a weird feeling...

In that case it unfortunately sounds like some kind of hardware fault has occurred with the DJI Air Unit following the crash. It might be worth opening up the Air Unit to see if the USB socket has been knocked off the board, or if there is anything else obviously wrong from a visual perspective. The video below which shows how to take it apart and what to expect...

Okay, thank you for the time you took answering and trying to help Took it apart yesterday already and everything looked fine inside, also the usb connector... If there is anything new to this I will post this here!

Often during a hard crash components get knocked off PCBs. And often upon visual inspection everything seems ok but then over time the issues start to surface.

I had a single crash on a quad once and upon visual inspection I just had a broken arm. I had a spare arm and replaced it.

On the first flight the Crossfire receiver was behaving weird and my range was like 50 meters. Replaced crossfire receiver and range was back to normal. I think the crystal oscillator went bad on it.

Now that I had RX range back to normal, my video issues started appearing and I would get static in around 200 to 300 meters line of sight. Bring the quad down but everything looks ok with the antenna connector etc. Replaced the antenna and everything was perfect. The antenna had a broken ground connection at the MMCX connector side.

And finally one of the cells on the lipo from the crash started loosing voltage over night and started getting worse oce the next couple of charge cycles.

Imagine, all of that from one crash.