Oh no. Did I just fry my Tx? (DJI FPV Hub)

[gavinski]

Bear with me - I'm no electrician as it will become clear.

Just received my new FPV Hub, ImmersionRC 5.8 Tx, IOSD Mini, Black Pearl diversity monitor, and spironet antennas. The hub is cool for easily connecting the iOSD mini, and the gimbal. But since I don't have the DJI Rx/Tx, I had to do some manual connections.

I followed all the instructions here:

http://download.dji-innovations.com...PHANTOM_2_FPV_HUB_Kit_Instruction_v1.0_en.pdf

"GND wire of analog video signal, connect it to the VIDEO_GND port of wireless video transmission module. If the video transmission module used has only one GND port on the transmitter, it’s alright to connect both GND and VIDEO_GND to the only GND port."

Thinking I had only one ground port on the Tx I connected both of the brown wires from the Hub to the black wire on the Tx, not realizing I had two GND wires on the Tx. I also connected the VCC red wire to the 5V out port (also red). Ugh.

When I powered on the Phantom, there was a "pop" from the Tx, and a burning smell. So, I am guessing that's not good. But I was able to get a staticky B&W picture, surprisingly enough.

Realizing I had all my wires crossed I connected the ACC and GND to the correct ports on the Tx. Now I get a better picture, which is color, but once I move a few feet away I lose it almost entirely. So something is wrong - or more likely fried.

And one more thing, I have just been twisting the wires together to test the connection (probably a non-no). I was planning to solder the wires tomorrow at my studio.

So, did I just blow up my ImmersionRC Tx? Or is there a different problem?

 

[goldfishrock]

Just to clarify, are you saying you connected a VCC to the 5v Out on the Tx (pin 1, red wire)? If this is the case then it sounds like you may have blown a capacitor on the vTX. The problem is that the output of the vTX is only a smoothed 5v supply while the voltage on VCC is 12v. To 'smooth' power, capacitors are generally used and as you may or may not know, if you accidently stick the V+ in the wrong end they go bang. I am guessing that's what the pop was that you heard.

The fact you still get a picture of sorts is because the main circuit is probably still intact however because of the way electronic circuits are 'balanced', by blowing the cap it won't be working as designed unfortunately.

You need to be very careful when it comes to connecting grounds to each other, especially when there are different voltage sources involved. The 12v VCC is capable of delivering 1.2A... which is a serious amount of current to put into a circuit in the wrong place. Twisting wires together is fine for testing as long as you keep them away from eachother and your plan to solder is the right one. Soldering gives by far a more surerior & reliable connection.

I believe the attached info explains what I think has happened.

Sorry i couldn't give you better news :-(

Subtract the lower voltage from the higher voltage. Add the internal resistances. Divide the voltage difference by the resistances for the current that will flow from the higher voltage source to the lower (this is why it's not a good idea - e.g. in the case of a non-rechargable battery it will do nasty things)
Multiply the current by the higher voltage sources internal resistance, then subtract the result from the higher voltage to get the voltage "between" the batteries (you can do this with the lower resistor/voltage source and add)

For example:
If we have a 10V, 10Ω source and a 5V, 40Ω source in parallel.
10V - 5V = 5V
10Ω + 40Ω = 50Ω
5V / 50Ω = 100mA
10Ω * 100mA = 1V
10V - 1V = 9V
So the parallel voltage will be 9V, and the current flow from the higher source to the lower source will be 100mA

 

[gavinski]

Thanks Goldfish for the detailed explanation. I think you are correct, for that's exactly what I did by connecting the VCC to the 5v Out on the Tx.

I figured it was now toast and ordered a replacement Tx. What an expensive lesson in electrical engineering.

 

[goldfishrock]

I'm really sorry to hear that :-( On the upside the damage is confined to a relitively cheap and easy to replace component rather than the P2 itself. Hope you have better luck with the replacement and if you need any advice, just shout

 

[gavinski]

Rather than get another Immersion Tx, I found the standalone DJI AVL 5.8 Tx and ordered that instead. I plugged the new Tx into the FPV Hub and it powered up no problem. But since the antennas I had ordered for the Immersion Tx (Immersion Fat Shark Spironet) had a male connection, I had to pull one of the antennas from my Black Pearl and put it on the Tx. The result is that I get a really fuzzy black and white image on the monitor. So a couple of questions -

Does the Black Pearl require both antennas to pick up a clear signal from just a few inches away?

Or is something else wrong here? Have I somehow fried this one too? (there may have been a brief moment with no antenna plugged into the Tx, which I discovered later is a no-no)

I know there are other threads on this topic, but what would be the best antenna solution for both the AVL 5.8 Tx and the Black Pearl Rx? For example, I have read good things about the Patch antenna from Fat shark.

 

[goldfishrock]

Hi mate,

The Black Pearl can operate on one antenna however being a diversity receiver it works best picking up the strongest signal through whichever antenna is picking it up. By removing one you won’t stop it working however it just won’t work quite as well as the way it was designed to.

Swapping the antenna…. What you are seeing could be caused by the differences between the one fitted to the receiver and the one on the transmitter. If they are the cloverleaf design you may find that one has got four lobes and the other 3. The four lobe version is meant for the receiver while the three should be fitted to the vTX. By you fitting one that’s meant for a receiver to the transmitter, you may reduce the transmission strength and quality. The best thing to do is get on eBay and buy a RP-SMA to SMA convertor (get a couple… they are dead handy to have). They should only be a couple of quid/bucks.

It could also be that you have antenna mismatch... that the antenna on your receiver is a different 'type' to the one on the transmitter. Are all of your antennas the Fatshark Spironet type?

Turning on a vTX without an antenna is a big no-no, how long was it on for before you realised?

 

[gavinski]

Thanks for the info Goldfish. That's good to know about having the right antenna.

I couldn't use either of theFat Shark antennas because they have the wrong connection (ie male), which is why I pulled one from the Rx.

The Tx was powered up without an antenna for maybe 30 seconds. Based on what I am seeing, I would guess this one is fried too. Since it was ordered as a single component, it came with no documentation whatsoever. It wasn't until after the fact that I tracked down the manual and saw the warning.

Hopefully others can learn from my mistake.

 

[gavinski]

Quick update that may help others:

Figuring I had fried the AVL58 Tx, I ordered another one. When I plugged it in (with an antenna fitted!) I still could not get a clear signal, even after trying every channel. Puzzled, I started looking more closely at the Diversity monitor and digging into the configuration menus. The I noticed that there are different bands, and I switched over to a different band ("F" I think) and boom! Picture!

Curious I tried the original AVL58 Tx and it works just fine on the different band.

D'oh.

 

[goldfishrock]

Hahaha.... oh well, at least you can return the other one and get your money back! :lol: Good news it's all working ok now.