Possible Diode Issue, Help Please.

Thread Starter

DrainMan

Joined Mar 21, 2020
2
I have a Hobbywing G3 Flight controller you can find a pic here https://www.myfpvstore.com/fpv-electronics/flight-controllers/hobbywing-xrotor-g3-60a-combo-fpv-stack-escflight-controller/

it will not turn on via direct power or via micro usb. I have checked for a short and can not find one. When i force in voltage one diode in paticular gets hot, it is next to two others but only this one get hot. it's a small SMD diode, the one that is getting hot is label SZ and the line is on the left side of the S and the 2nd diode is also labeled the same and the third is labeled 1H

I am still learning and really enjoy playing with electronics, any help would be appreciated. Thanks in advance!
 

Alec_t

Joined Sep 17, 2013
11,146
Welcome to AAC!
it will not turn on via direct power or via micro usb.
Where are you applying "direct power"?
The USB port is only for flashing the firmware or adjusting parameters: not for use as a power input.
What do you mean by "When i force in voltage "? That sounds like a recipe for disaster.
Some diodes may be signal diodes and run cold, whereas others may carry high currents and feel uncomfortably hot yet be well within their power-handling rating. Without a schematic of your FC we can't tell whether the diode you have concerns about is behaving normally or not.
The label 'SZ' suggests it may be a Zener diode. Then again, it might indicate something entirely different in Chinese :).
 

Thread Starter

DrainMan

Joined Mar 21, 2020
2
Welcome to AAC!

Where are you applying "direct power"?
The USB port is only for flashing the firmware or adjusting parameters: not for use as a power input.
What do you mean by "When i force in voltage "? That sounds like a recipe for disaster.
Some diodes may be signal diodes and run cold, whereas others may carry high currents and feel uncomfortably hot yet be well within their power-handling rating. Without a schematic of your FC we can't tell whether the diode you have concerns about is behaving normally or not.
The label 'SZ' suggests it may be a Zener diode. Then again, it might indicate something entirely different in Chinese :).
Thank you so much for your response! The flight controller wiring diagram tells where to input voltage, I have applied 18v the max is 25.2v / that is all i meant by forcing voltage, because it's not working yet i still had it on 18v but with my bench supply which has fault protection. Direct power is just my poor explanation of putting power in where you are supposed to turn it on at. I strongly wish there was a way to find a schematic as well, not sure if there is a way to get one, it is a Chinese made board so I don't think they ever made one. I have other drones that use the same FC and this diode doesn't get hot, and this FC won't turn on, when you connect the USB to the computer the board is supposed to turn on and allow communication and it does not do that, that same diode just get blasting hot. I used the multimeter and I OL. in one direction and I get .183 in the other so my first thought is that it is good and I just need to find out what is causing it to get so hot, I just don't know the next step in trouble shooting this circuit. Thanks again Alec for any advice you can lend.
 

Alec_t

Joined Sep 17, 2013
11,146
If you have two identical FCs and the corresponding diodes behave differently it suggests the one that gets very hot is carrying more current than it should. So something down stream is presumably at fault. If you trace out the relevant part of the circuit it may lead you to the culprit.
 
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