Problem with overvolted devo7e

Hi guys,
I'm in a bit of trouble. I had a devo7e working like a charm but unfortunately i had a bad idea to put in it a 7,4v 2s lipo. After a little bit i turned it off and now when i turn it on also with a 4x1.2 batteries screen light blinks once and then it goes off.
I think some power up smd component has blown out, i have skills to replace them but (my bad) i am not able to detect the problem. Any advice would be appreciated. I can smell a little bit of burnt on the right side of on/off pcb connector in the center of the pcb board.
Thanks in advance.

Here is a pic of the pcb.
drive.google.com/file/d/0B9v998Jbj7ltcnN...RTg/view?usp=sharing

I have tested ss14 diodes on the left side of the pcb and they seem to be ok

I have found the Y1 and Y2 transistors are SS8050 and SS8550, need confirmation.


Does anyone know which is the name of this component?


As i see, on it , it's written F1CJ3 or something like that.
Probably it's a mosfet.

You see those 2 through holes just below that component? Can you hook the battery back up and try to power it up and check voltages at those two pins?

The GND is the right hole, am i right?

edit: Stupid question. Actually i can test it with the multimeter. I will try as soon as i get home. I will test voltage at those points and report back.

Thanks for reply.

I have tested those 2 holes and i have a 4,28v current from a 5,24v battery pack. So i think diodes are working just like they should.

Any other advice Cereal? Do you know the name of the smd just on the top of those two holes?

Thanks a lot for helping.

I think it might be the small 3v3 regulator, it is the 5 pin smt component very small located in between the two capacitor cans. This component normally gets very hot at 100mw power. It could be it burned in your case?

I unsolder this onboard miniature vreg and replace it with 3v3 stepupdowm regulator from pololu it is a very tiny pcb regulator wich makes 3v3 from 1.5v input to 12v.

I can confirm my devo 7e can run on two 18650 without damage also volt being displayed in display.

I thought about it, my problem was that probably i overvolted it more than 8,4v. I don't know the regular behaviour of that smt so i can't tell if it is the problem. Do you know how and if i can test the pinout? As i see with my multimeter the L04B smt is giving me 4-5v from lower-right pin(the one going into 8pins chipset before cpu) instead of 3v as you said. Do you think ARM cpu is burned because of that? Any ideas on how to proceed?

Ehi guys, i've found now that my vdd point is shorted with GND (ground), can someone confirm that? Is that normal?

eikaf wrote: Ehi guys, i've found now that my vdd point is shorted with GND (ground), can someone confirm that? Is that normal?

I don't currently have a Devo opened to meter but by definition Vdd is positive supply.

What is MAX voltage for 7e?

It's stated from specs 7.4v but to me something went wrong, I think I have broken arm CPU. Do someone know if it's possible to replace it and flash it back? Do someone have ever tried it?

Yes, you can replace the CPU chip. It's an SMD chip, so you need the tools and skills to do that.

You'll want to flash the walkera bootloader on it. There are instructions for doing that in the forums as well, but I'd be tempted to try that before installing the chip in the 7e, as I've not had much luck getting an installed chip into the native bootloader. Come to think of it, you might try flashing the walkera bootloader on your existing chip before replacing it. Thast might fix things if the walkera bootloader is fried, and you'll need to figure out how to do that either way.

After that, you should be able to use the standard install path to reinstall deviation.

Thanks for the advice, actually my problem is that I have a short circuit between vdd and gnd and I can not figure out what's the problem. I have noticed that the components on top of the cpu are also shorted, also the two pins coming from cpu and going to the small capacitor are shorted.

I think I can't try to flash the bootloader since I have this problem.

@Fernandez you have a pm.

@Anyone who know this. What about installing 3v3 pololu instead of AMS1117 why would you prefer the first one?

Is The POLOLU the one with this code: D24V10F3??

Thanks.

I would just get new one its 50 - 60 USD and use this one for spares.

For sure, I just wanted to ask how to mod the new one with 3v3 voltage regulator, ams1117 or polonu one.

I have replaced the stock small regulator in the devo7e by this one:
www.pololu.com/product/2122
Pololu 3.3V Step-Up/Step-Down Voltage Regulator S7V8F3
It creates a stabilised 3v3 without getting hot, input range 2v7 to 11.8V and efficiency 90%

How to do it....
Unsolder the small 5pin stock regulator, it is located between the 2 electrolytic capacitors, just remove and leave it out.
Solder vinput of the regulator to the pin above the Cap, see photo.
Solder gnd to the Tx module shield
Solder 3v3 regulator output to the 3v3 Vdd pin of the stock tx module.

The Pololu pcb, I just fixed it on top of the component with some hotglue to hold it in place.
see photo


I have allready modded my battery tray of my 7e and can confirm 2 18650 3400mah cells do fit the tx, and I am still back wards compatible and can use the NiMh original tray.
Next mod will be to put two of these:
www.banggood.com/NCR-18650-3400mAH-3_7-V...nasonic-p-72906.html

I saw another old post from you, where you changed regulator with ams1117, which is the difference with Pololu one? They are not this easy to find here in Europe.

The AMS1117, works indeed also but downside it has dropout voltage, i do not know excact but about 1.2V?
TX therefore must not drop below 4.5V to be safe? If go down too low, you risk the Tx will full stop go fully out......

When using the Frsky D protocol I have instable Tx voltage readout sometimes fluctuates by 0.3Volt.
I am sure that the voltage itself at the ADC pin of voltage devider is stable, I tested with 10UF capacitor, but still fluctuates the Volt readout.
Due tthis fluctuation, battery low alarm needs to be pretty high to be reliable. I really hope we found the reason for htis and can get it sorted.

Anyway using the polulo step up/down regulator, you can be 100% sure what ever the state of the Battery the Tx will keep running 3v3 at all times, no dropout voltage.
So I would recommend use that one.