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One of the motors turn on as soon as battery is plugged in?!

SJLPHI

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Hello,

I have two tellos. One was always a bit "off" and I deemed "defective" because the suppliers was dishonest and it came with an extra screw stuck to the motor, and another one that always flew well.

I call the defective drone the "A" drone. It was my first Tello and I bought it "new" but it obviously had signs of refurbishments and in Switzerland return policy isn't as liberating as in Canada or U.S. so I took the loss and kept it.

My A drone has been flying for about 100 hours, and had 6 motorsreplacements. I now have the weirdest problem. Since the last flight, one of the motors turn on immediately as soon as I plug in a battery!

Just before that, I switched out one motor that was heating up unusually and the batteries ran out in ~5 minutes instead of near average ~13 minutes.

I checked the circuits many times over and there is nothing from the PCB to motor contact that is shorted. There is no analog contact that should turn the motor on when I plug in the battery. The flight processor has been under some intensive heat but could that actually cause a malfunction like this?

I am grounding my A drone for now but I have a really hard time figuring out what's wrong with it. Now the camera doesn't work anymore and the drone barely turns on. It seems like A drone is finally toast and time for B drone to fly again.

Any clue on how to repair my A drone? For now, I've salvaged all motors, and I will take out the PCB entirely to work on it.
 
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agraham

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Since the last flight, one of the motors turn on immediately as soon as I plug in a battery!
As it is unlikely to be a software problem I would guess at a short circuit driver transistor, or a similar hardware problem. Unless you are a real electronics enthusiast I would think that the motherboard is toast. You can probably reclaim the camera and infra-red module if needed.
 

SJLPHI

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As it is unlikely to be a software problem I would guess at a short circuit driver transistor, or a similar hardware problem. Unless you are a real electronics enthusiast I would think that the motherboard is toast. You can probably reclaim the camera and infra-red module if needed.

I actually have been recently practicing soldering small boards and have a bag full of transistors in similar size as seen on the Tello board. Thanks for the suggestion.
 

Flydrone

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8846QM active chip responsible for power supply I have not thoroughly examined the pcb
but you could try to replace it
 

SJLPHI

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It will take... a lot.... of practice soldering before I can replace that.
 

Flydrone

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Sweet! I don't know how you know this but I will certainly try.

I'm not 100% sure if this is the cause of your problem ... but this cips if you see on the internet seems to be for power management. to support it you will need a hot air soldering station.
 

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Flydrone

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certainly a rather complicated job ... but since the drone is not working, it is worth keeping to do some tests ...
to unsolder and re-solder you will need flux for smd.
 

jakebrandon023

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Found the cause. It's a busted dual transistor(square, 6 legged). The engravings were "1C" and "W82" below it.

Only one of the 4 transistors heat up when battery is inserted. And if a transistor is damaged, it loses its ability as a switch and remain ON making the motor spin when battery is inserted

Unfortunately can't find a replacement of it anywhere on the internet.

My drone won't fly because that one motor with the busted transistor spins at a constant speed all the time. I'm wondering if it's possible to bypass the busted transistor with jumpers so the motor speed can still be controlled instead of constant speed so my drone can atleast fly.
 

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