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Shorted components near antenna amplifier

punkkone

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Hi guys! I know this might be the wrong part of the forum, but I figured I'd have a higher success rate with asking people that are not afraid to take stuff apart :)

So, I bought a crashed Mavic Pro, front was badly smashed, front sensors, gimbal, shorted and burned camera board, torn ribbon cables.. I tried starting it up, and it just gets stuck on solid red light, no wifi or USB connectivity at all. I thought "well, that could be anything.." and placed an order for most of the parts that were obviously beyond repair.
What caught my attention here is that the motor startup motor-"jiggle" only moved the rear rotors, the front ones kept still.. Possibly an ESC board issue? And I'm fine with just replacing the ESC board as the prices are reasonable.. So I took the rest of it apart and found this.
After carefully cleaning the board and removing the shield for the wifi amp etc:


20190911_141615.jpg20190911_140809.jpg

Now I cannot for the life of me find what those IC:s marked "S 20" are? Or the components between the antenna connectors and those IC:s? So, what would be the most likely culprit for blowing the IC:s (or possibly the IC:s are just damaged by the resistors blowing out..)? What are those components? I'm willing to have a go at replacing the components before ordering a new core board as they are not exactly cheap..

Feel free to move the thread if it fits better somewhere else.

Cheers!
 

punkkone

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Mm, yes that was my initial thought, but I've been searching for hours and hours and I can't find anything that resembles these. The inputs seem to be the two corners on the side opposite of the corner marking, and the output the center pin on the side with the marking no?
Finding direct replacements would be very very neat...

Any idéa of what the components between the IC:s and the IPX connectors are? Looks like either some coil or a female connector to me?
 

punkkone

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Hey, what if the "S 20" is just a divider/combiner? That'd make sense.. A lot of more sense as there is a "S 20" north of one of the burned ones but not the other.. Hmm
 

AMann

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Mm, yes that was my initial thought, but I've been searching for hours and hours and I can't find anything that resembles these. The inputs seem to be the two corners on the side opposite of the corner marking, and the output the center pin on the side with the marking no?
Finding direct replacements would be very very neat...

Any idéa of what the components between the IC:s and the IPX connectors are? Looks like either some coil or a female connector to me?
Antenna tuning caps? Are they really fried? Looks like they are glued down after adjustment. I’d check their values before pulling them.
 
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punkkone

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The left one is fried for sure, all carbon gunk from melted plastic on the inside.. The one on the right is seems to be ok, measured continuity and resistance. I really don't get how this damage can even occur.. The drone is not water damaged, no obvious shorts except where the front sensor ribbon cable connectors were smashed, there I could see signs of a pretty bad short.

I mean, was the previous owner flying this in a thunderstorm or did the drone come in contact with power lines? xD (of course not, but it's just so weird)

But ok, if those are just pots (they are very very tiny) I could probably just bypass them and come back to that issue later. But the "S 20" conundrum is the big issue, the closest thing I can find, to what I believe them to be, are these: https://ww2.minicircuits.com/pdfs/SP-2U2+.pdf

Never came across a more elusive IC.. I might just roll the dice on getting a known bad board and transplanting the IC:s from there :/
 
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AMann

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The left one is fried for sure, all carbon gunk from melted plastic on the inside.. The one on the right is seems to be ok, measured continuity and resistance. I really don't get how this damage can even occur.. The drone is not water damaged, no obvious shorts except where the front sensor ribbon cable connectors were smashed, there I could see signs of a pretty bad short.

I mean, was the previous owner flying this in a thunderstorm or did the drone come in contact with power lines? xD (of course not, but it's just so weird)

But ok, if those are just pots (they are very very tiny) I could probably just bypass them and come back to that issue later. But the "S 20" conundrum is the big issue, the closest thing I can find, to what I believe them to be, are these: https://ww2.minicircuits.com/pdfs/SP-2U2+.pdf

Never came across a more elusive IC.. I might just roll the dice on getting a known bad board and transplanting the IC:s from there :/
I think you are right, maybe its a RF splitter/combiner on the final. I didnt think there was enough output power to do it, but I wonder if all that can fry like that if the antennas are damaged or disconnected?

Or if there is no sign of water being inside it, perhaps something conductive entered the drone (like glitter can do it), or perhaps there’s a cold solder joint?
 

punkkone

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I think you are right, maybe its a RF splitter/combiner on the final. I didnt think there was enough output power to do it, but I wonder if all that can fry like that if the antennas are damaged or disconnected?

Or if there is no sign of water being inside it, perhaps something conductive entered the drone (like glitter can do it), or perhaps there’s a cold solder joint?
Possibly, the left antenna housing is broken clean off and the antenna is dangling freely. Never seen actual board damage due to shorted/damage antennas/coaxial cable though but I guess it's possible. The attenuation/resistance for the complete circuit might be way off with a shorted antenna, but I haven't studied the circuit closely enough to determine if that might be the culprit yet.

I'm wondering what would happen if I just desoldered the damaged components and hooked antennas directly to the wifi-board. Sure RF mode wouldn't work, but it might let me test other things when all the other broken components are replaced.
Wouldn't surprise me if it gets pissed because gain levels would be out of spec but who knows..
 
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