Unexpectedly bunch of AIO FC dying on me.



#1. JHEMCU GHF411
USB: No LED. SOT353 "WJ=3" super hot in 1sec.
LIPO: 5V measures 5V. 3.3V measures 0.9V. First half of ESC chime.

I'm guessing this is the 3.3V LDO thats fried - I need help finding this part or replacement.
Alternatively it could be a shorted cap, or dead MCU right?
Should I remove the F411?



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#2. JHEMCU GHF405 - almost working
USB: has LED and connects to USB. 
LIPO: 5V measures 5V. 3.3V measures?? no pad.
Motors do complete BLHeli chime. When you arm, motors kinda stutter. after 5-10 sec, beep-beep turn off. 
The SOT353 SMD with marking L303 on back under gyro is super hot on LIPO.

Anybody got similar symptoms?
Whats next step to diagnose?



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#3. HIFIONRC F7
USB: No LED. 
LIPO: 5V measures 5V. 3.3V measures 1.1V and slowly climbing.
I removed the about 6 capacitors that looked liked shorted.
The RX1 pad was 46ohm to Gnd and 3.3V. After I removed the F7 MCU, I get the red power LED
I ordered replacement F722.

#1 is fixed - not quite....

Removed the two shorting caps next to LDO. Still problem

Noticed its a short on the LED pad too - so 90% its bad MCU.

Removed the LED wires. Still problem.

Removed the MCU. Problem went away.

Replaced F411 from donor board. Completely dead.

Replaced F411 from 2nd donor board. WORKS.
Well at least it looked like it worked. The blue red LED flash.
I was able to connect to Betaflight. But it shows NO GYRO. OMG.

The input voltage in Betaflight shows 6.0V.. so something is still clearly wrong.

#1: are you sure the top marking is “wj=3”?
The reference list below is a great resource for figuring out what you’re looking at:
http://www.dl7avf.info/charts/smdcode/cw.html
Don’t remove the f411. Remove the ldo- then probe your way backwards from the Ldo’s input to check your voltages.
It’s possible that a cap shorted to ground, but the most likely culprit is the ldo/regulator that you’ve already identified. If you’re concerned about a cap, you can test it in circuit with an lcr/esr meter. If you don’t have one, you can get a cheap diy kit from eBay for less than $20. They’re super handy.
Anyhow- think about what could cause that component to heat up: 1. faulty component itself (most likely) 2. Faulty component prior to it causing it to receive far more voltage than it can handle (unlikely, but if this is the case, you’ll identify it when you probe backwards from its input- also, you’ll want to replace it if it did receive too much voltage) 3. Something shorting out after the ldo that is causing it to pull a high load through the ldo (this is unlikely because with the exception of caps, most components fail open not short- I’m not saying your mcu isn’t dead, but if it was, it wouldn’t likely be the cause of that thing heating up)
You can rule out number 3 by checking the output voltage of the ldo before you remove it.

I’ll come back later this evening and try to find you good replacements- I need a few myself. I don’t know where you’re located, can you order from mouser or digikey?

#1
It likely was the MCU that was fried. After I removed it the short went away.
Also with replacement F411 from donor board LED lit up and it connected to Betaflight.

buttt....

its dead now (AGAIN).

I tried to reflow the F411. I shifted it a bit, and also knocked off the tiny resistor and cap next between MCU and gyro.
Now same symptom as before. No LED. LDO super hot. No connect to BetaFlight. I think I fried this MCU.

Im 99% sure I fried the F411 because alignment was off.
Now I need to order like 3 (incase I screw up) :/=

#1
Magically its not fried.

Oh what a nightmare.

Took off the donor F411.
I thouroughly cleaned the board.
Took off the super tiny 0201 resistor and caps
cleaned pads.

lost the tiny resistor!! Had to crack open other drone with GHF411 to find its value. Got a donor. soldered it.

Now re-soldered the F411.
Magically it works now... USB LEDs. Connects to BF. And gyro is there too.

#3
waiting for replacement F722 shipping

#2.
0 progress. No idea whats wrong.
5V and 3.3V look ok. Connects to BF.

Complete ESC chime. Even on motors tab, motor stutters and then beep-beep turns off.

That SOT353 is fricken scorching

Board #1 connects to USB, and flashed to correct target.
It looks like working correctly.

But, when I arm, motor4 only slow spins and then stops.
There is no error beep-beep.


When I am not super busy at work, I will try to diagnose board #2 again.
Probe the pins.
Check if other donor board has same size 5V.
Replace it.

When 3.3v is short, that's almost always the processor being dead. The regulator gets hot because it's essentially shorted at that point.

#1. I replaced the F411 MCU. Nothing obvious why it would slow spin motor. Maybe replace gate driver or even BB2.

#2. I msg emailed JHEMCU about the hot vreg to identify the part.

#3. Replacement F722 arrived. Wow its a fast pacific ship.

I ended up replacing all 18+ 0201 for motor3 and motor4.

I swapped BB2 and Fortior from donor board.

Even more broken. Motor4 no BLHeli chime.. just jerks a bit. No spin

Did you ever hear back from JHEMCU on the identification of the part for #2?

If you're still trying to identify the 3.3v LDO marked "wj=3", I *think* that it is a Richtek RT9013.
https://www.s-manuals.com/pdf/datasheet/...ichtek.pdf

(22-Aug-2022, 08:21 AM)Lemonyleprosy Wrote: Did you ever hear back from JHEMCU on the identification of the part for #2?

I have the model numbers for the SMD marking on different thread. L303 = SPX3819. 500ma 3.3V LDO
Takes approx 9V from linear regulator SOT89 marked 8K***.

I ordered replacement.

But maybe sonething wrong with BB2 or Fortior.... but it does BLHeli chime

Maybe lift output leg and connect different model 3.3V LDO in parallel?

Other donor boards have different LDO.. interchangable??

I’m still learning, but I don’t think they are interchangeable.
Some 3.3v ldo are fixed output voltage, some are adjustable output voltage (adjusted by changing value of a resistor), and some have max 5.5v input.

I think you would have to compare datasheets, and potentially change a resistor value.

I could be wrong, as I said, I’m still learning.

I used hot air to remove F7 from HifionRC F7, and replaced with blank F722. Need lots of flux and patience, because need to make sure all the pins flow at same time.

Short circuit tests OK. Connected to USB. Only red LED. Good.

I hooked up STLink V2 to pin46 and pin49 SDIO and SWCLK and 3.3V and Gnd. Full Erase. Flash Betaflight 4.3 F7.

Still only red LED. The USB plug is full of flux. Took forever to scoop it out. After I connected to Betaflight, I flashed HifionRCF7 target. Everything works!!

Excellent! Good job!

I need to pick up some blank mcu’s to fix a couple boards, but I’ve been hesitant to because programming them sounded a little intimidating to me.