Nedd help : Devo 7e powering issue

Hello all,
following this great forum since a while now, I did several mods to my Devo 7e.

One of these mods was powering with a 2s lipo pack, which I did 3 weeks ago. It worked perfectly so far.

Last week I implemented PWM input from potentiometes + arduino nano. Worked also perfectly last week end.

Today I powered my Tx, but no reaction. No buzzer and no screen.

After some checking, symptoms are following :

- impossible to power the devo via the power switch.
- If I leave the power swith ON, I can power the Tx by unlugging / plugging the battery pack. it works every time.

Any idea on what is happening and how to solve this ?

Thks in advance

Adding some findings :

when battery is plugged and power swith is off, the tx module is powered with 3.3v. Actually looks like all the 3.3v points are constantly powered. Looks weird...

Actually I could decide to hook the power switch directly on the battery power wire, which would make it work fine. But I don't know whether it would be very healthy ??

sounds like the extra voltage has killed something. also the rf module should be fed ~5V not 3.3v

From the description of your problem, it could be similar to the FET problems we've been seeing. In your case it could be internally shorted and not actually burnt. Check out this post and test/replace that component. You could also trace the pins on that component to 2 other transistors that make up part of the switch mechanism.

http://www.deviationtx.com/forum/6-general-discussions/5952-devo-7e-main-pcb-component-id-help

This diagram form the downloads section may help.

devo8-power-switch-circuit

thank you all fo the hints. Will check this when I get time.

I understand that one should limit the maximum voltage to feed the 7E. Although some of us can feed it from a 2S lipo âck directly without problem....

What should I do to avoid this problem in the future ? (would need something simple...). Shall I use a BEC finally ?

Some have been successful with using a BEC, but personally I've not done that so can't really say. For me, I charge my 2s pack using the storage setting of 3.8V per cell so 7.6V total. I then use them until the pack hits 6.6V (3.3V per cell). I've not had any problems thus far that way. Probably not the best way as I don't really maximise the lipo, but I'm not risking it until I have a better solution (which I don't).

Have you actually managed to fix things yet?

Hello,

Maybe a bit more help, I'm not an expert in electronics...

1) I've tried this :

Switch on the power : nothing happens. Then I short the source and gate of the PFET : my 7E wakes up ! Does this prove that the component is dead ?

2) If I have to replace it : I have several dead motherboards. I have found the schematics of one of them, and have identified this component :

TP0610K

Would it be ok as a replacement for my 7E ?

thks in advance

I have some 3000mah AA li-ion's en route to my house atm, these li cells have a switching vreg inside each cell and they hold 1.5v until ~90% depleted then drop to 1.1v to let you know they need charged. they are about half the weight of nimh's and if course have the usual li cell attrubutes of low self discharge etc. I'll be making a post on them once I've tested them and I'm happy with the performance. this way you get all the positives of li usage without the downsides of blowing components

Thanks Harry, but now that I've moded the frame to hold a lipo, I would have difficulties to come back to AA batteries.

Harry I have also some ideas in my mind but no time yet to work it out.

I managed with a few modifications to the battery holder of 7e to fit two of these lion 3400mah cells:
www.banggood.com/2PCS-NCR-3400mAH-18650-...Battery-p-87078.html
It is a non permanent mod, meaning you can also still go back and fit the original battery holder.
Then I intend to put both of the cells in parallel, basically run the Tx on 1s.
To do that reliable I use step up/down convertor this one, giving 3v3 even for input voltage lower than 3V.
www.pololu.com/product/2122

To charge the lion cells I intent to do that via the usb port on the TX. By installing this tiny circuit.
www.banggood.com/USB-Lithium-Battery-Cha...ection-p-924048.html
The charger port wont be used anymore.

One of the issue is that when the devo power switch is set to off it still runs to store save the memory, at switch off. The polulo regulator has a SHDN switch pin, I thought possibly using a capacitor discharge, r/c combination it could be used to power on off?

---

The SHDN pin can be driven low (under 0.4 V) to power down the regulator and put it in a low-power state. The quiescent current in this sleep mode is dominated by the current in the 100k pull-up resistor from SHDN to VIN. With SHDN held low, this resistor will draw 10 µA per volt on VIN (for example, the sleep current with a 5 V input will be 50 µA). The SHDN pin can be driven high (above 1.2 V) to enable the board, or it can be connected to VIN or left disconnected if you want to leave the board permanently enabled.

---

Than all the regulator stuff power network on the devo etc not anymore needed, we can bypass.
Also I hope to fix this instable Tx volt readout on the devo 7e.
One question is dow we also need to install a 5v Polulo for the 7e main module?


This idea might also be of interest for the future deviation using ARM development bord.

Ben5757 wrote:
2) If I have to replace it : I have several dead motherboards. I have found the schematics of one of them, and have identified this component :

TP0610K

Would it be ok as a replacement for my 7E ?

If it can be of any interest, I did the replacement and it works. Will have to wait to see if it holds the voltage on the long run. Datasheet mentions 60 volts.... . Fully charged the Lipo pack and seems to manage it.

Brgds

silpstream wrote: From the description of your problem, it could be similar to the FET problems we've been seeing. In your case it could be internally shorted and not actually burnt. Check out this post and test/replace that component. You could also trace the pins on that component to 2 other transistors that make up part of the switch mechanism.

http://www.deviationtx.com/forum/6-general-discussions/5952-devo-7e-main-pcb-component-id-help

This diagram form the downloads section may help.

devo8-power-switch-circuit

请教你一个问题，devo8电压取样电阻在MCU哪个引脚？原谅我这糟糕的翻译T_T
Ask you a question, which pin of the devo8 voltage sampling resistor is in the MCU? Forgive me for this terrible translation T_T