Advanced tiny resisters replacement help

[Hoppinrocks]

Hi guys, found someone to try and repair my motherboard. I need to replace a few of these little resisters but need to know their values or exactly what I need.
They did not blow but damaged by the last owner trying to open the shell.
Please and thank you.

 

[epicdoom]

as long as they aren't blown you can remove them read the values with a multi meter to find the values if they are still holding value they are still good just re-solder them back in place

 

[Hoppinrocks]

They are broken..

 

[epicdoom]

ok can you see the traces they sit on are they all attached to the same trace on the PCB ? if they are then measure the value of each one that is still intact I have a feeling they are all the same value if they are in the same string they are in a circuit called a load

 

[HaJaa]

I just could not believe....
@Hoppinrocks you have almost exactly the same problem as me. I think we can help each other

My story:

I was flying my P3ADV v2 on Litchi app with autopilot. Part of the route was planned beyond of the transmitter range. I knew that I lost control for 45 seconds until the craft returned from the loop. The furthest point was 3.7 km from the RC. I have been flying this path many times and I knew that perfectly. That is why I allowed myself to modify the path live with the sticks during the execution. That day weather was very strange. Did I mention that in the midst of the distance between the RC transmitter and the craft there is a high voltage line? 110 kV at an altitude of 125m ? I pulled up long long before the critical point but this time I lost the signal earlier than ever. The autopilot tried to pull up but suddenly the birch-tree grew right out of the path. ​

ok, I overdid the length of the description. Let's go back to the case. Here is my only damage:

Missing elements could be capacitor or resistor even coil. I am a programmer not an electronics engineer, but simple soldering and electronics repairs have always attracted me very much. I wrote long inspirational letter to DJI support asking them for help:
"Dear DJI team. Please help me determine what elements should be in places #A and #B (marked in the photo). I have the right soldering equipment and skills.... ...For you it is a matter of looking at the matherboard scheme..."
The response was (as you probably expect):

"With regards on your inquiry... bla, bla, bla... we do apologize but ...bla, bla. ...DJI Technical Support cannot mess with motherboard... haha bla, bla, ...repair is not as easy as you think... "
Stupid ignorants! Talking to them is a waste of time...

First I noticed that the missing SMD elements are from one of engine controllers. There are four on each mainboard. So using motor M3 controller I can see what is missing on M2:

I spent tons of time looking for pictures, diagrams, tips in different threads on different forums, comparing photos etc.... I was close to give up and order broken ESC mainboard (DJI part 96) to transplant the missing SMD elements.
Then I found great github repository by mefistotelis.

It is awesome, see it: P3X ESC center board · mefistotelis/phantom-firmware-tools Wiki · GitHub
I found what I was looking for:

I discovered that my missing SMD elemets are 100nF capacitors. It is very useful because it is not possible to mesure capacity without unslodering the element. In oposite to capacity we can measure the voltage on board. It is 63,2 mV:

I ordered new capacitors 100nF 62mV as it is very common SMD part. Unfortunately it occured that the size of spare part is 3 times bigger than I expected:

I stopped on this. I know that very small SMD elements have no inscription. To find the element details or name you have to measure it and look to the SMD elements catalog to find the right one using L x W x T.
Probably (I'm guessing) need a capacitor with the same parameters but in another different housing?

I tried to measure small capacitors without unslodering it from the mainboard. It is very difficult
I think it is 1,08mm (L) x 0,5mm (W) I dont know how tall it is. It seems to be 0,4mm (T) but I did not measured it, so it is my guess as well.

Any hints and tips are very welcome

 

[Pharm]

I applaud your determination as I’m afflicted with the same issue (not the electronic issue but the issue of being determined to fix things instead of buying major replacement parts). I once spent several weeks tracking down some IC timer chips to repair an x-ray processor. I was determined to avoid spending $800 for a proprietary replacement circuit board. In the end, my repair didn’t work. I finally hung my head in shame and paid the $800. My only respite was that I refused to pay the $200 labor/repair fee. I replaced the board myself (a 10-15 minute job) and all worked well.

Not saying you should throw in the towel or hoist the white flag yet but you might want to at least add that to your list of options.

 

[epicdoom]

here is an idea also is no one is willing to tear down a drone to get you the values look on ebay for the motherboard if you find one ask the seller to measure the values for a small fee he has nothing to loose doing that for you and in the end makes more for the sale of the board. option 2 buy one from amazon measure the resistors and send it back.

 

[Steve7777]

Also no expert, but some of the physical sizes of these smd 100 nF capacitors seem to be closer to what you're looking for.

100 nF capacitor smd | eBay

 

[epicdoom]

Also no expert, but some of the physical sizes of these smd 100 nF capacitors seem to be closer to what you're looking for.

100 nF capacitor smd | eBay

that's kind of an issue because Many SMD SOT size components are hard to distinguish if they are a resistor or a cap the only real way to know is test them. a resistor will hold its value say 200ohm your meter will settle on or very near that value and remain there. a capacitor will show a resistance and start dropping in value with leads in one direction and climb in value if you swap leads. but it wont remain steady. once you know if its a cap or not you can then determine the caps value with equipment for that purpose.

 

[quaddamage]

I know that very small SMD elements have no inscription. To find the element details or name you have to measure it and look to the SMD elements catalog to find the right one using L x W x T.
Probably (I'm guessing) need a capacitor with the same parameters but in another different housing?

Yes, different housing. Housings of SMD elements are standardized. Looking at your new part, you probably ordered 1208 or 0806. You probably need 0201. See here for details:
Surface-mount technology - Wikipedia

EDIT: based on the measurement you provided, you need 0402.