QX7 dead after accidentally supplying power to the trainer port.

[ninjazx11]

Solved!! See my post below.

Hi all,
I wanted to use head-tracker on my qx7 via its trainer port but the trainer port doesn't supply power to the head-tracker. So i tried to install stereo jack so that i could use power,signal.gnd.

I used power and gnd straight from the batt connector and took signal from the trainer port.I selected tip as signal,center as gnd and the 3rd as power.

So what happened was that the 3 pin stereo jack i used somehow shorted the power to the signal while inserting it into the jack.I purposely selected tip as a signal and center as a power knowing that while inserting, the last 2 can get shorted but never expected that the 3rd pin can also get shorted to the signal.

Now my QX7 is not booting anymore.My batt voltage was around 7.6v at the time of short.Any ideas please.
Not sure if i need to replace both main and RF board or just the main board.Please help.Thanks.

[jhsa]

That was a very bad idea, specially if you inserted the jack with the radio turned ON. I don't have a QX7 but if you connect your radio to the PC via an USB cable, does it see the radio?

João

[ninjazx11]

Yes that was my stupid mistake:(

No PC is not seeing the usb of radio.I just hear a click from the speaker when i insert a usb cable or when i push the power button.

[jhsa]

You might have to open it and check if you have some blown component or track. I think you might have shorted the battery voltage.

João

[ninjazx11]

Already checked it and didn't find anything abnormal.Looks like its toast..(

[MikeB]

If you shorted the battery voltage to the trainer signal, then you most likely connected the battery voltage, via a 100 ohm resistor and a 1N4148 diode to the main 3.3V supply. This will almost certainly have damaged the processor, probably the SD card (you could check that by trying it in a PC), and maybe other components on the main board. The Rf board is probably OK as that is supplied with the battery voltage via a MOSFET switch and has its own voltage regulator.

Mike

[ninjazx11]

Thanks MikeB for your reply.

I just checked SD card and its working.So I will order the main board then.Any place to get cheap board?I just checked banggood got in stock for $66.

[ninjazx11]

Hi Mike,
Do you think it's worth trying changing the processor if there is no special programing involved?I got hot air station, hakko fine soldering iron and a chip quick.If I replace the processor, will I be able to load the opentx firmware via USB? Thanks.

[Kilrah]

If nothing else is damaged yes.
The LCD might have taken a hit as well.

[ninjazx11]

Okay then i am gonna try and take a chance.

Existing processor says STM32F205 VET6 but only STM32F205 VET7 is available at my store.Will it be compatible?and what about boot-loader and stuff?can it just be programmed again by connecting via USB?

[Kilrah]

Can't find the difference between T6 and T7 if any...

Yes you can flash through USB with power off.

[MikeB]

T6 = -40 to +85 degrees operation range.
T7 = -40 to +105.

Mike

[ninjazx11]

Thanks Mike and kilrah.Going to order the processor chip.
One more thing I noticed that insertion of trainer plug,breaks one connection on the jack.Does it indicates the processor that plug is inserted??
And what type of plug we suppose to be using?I mean stereo 3 pin or 2pin mono?

[Kilrah]

Both 2 and 3 pin work, and yes there's a detection contact. And no, NEVER use a jack for power, everything shorts to everything during connection.

[ninjazx11]

Guys Success!!

Thanks for the help and encouragement!!My radio is alive now:) I used chip quick and hot air to remove the processor from the board.I tell you that pads on this board are very fragile.Even thou i made sure that chip was freely moving before i picked it up,somehow i lifted one trace on the corner as you can see in one picture.But luckily it didn't break and i folded it back and soldered.Just curious what that corner pin is used for?Just in case if i had broken that connection,what function would have effected?

I used around 280 deg C hot air + chip quick to remove the bad chip.First i tried using solder paste but it wasn't working well(i think my paste was too old and expired).Then i used solder drag method using soldering iron @ 230 deg C and it went okay.Then I just used copper braid to removed solder bridges.Processor chip costed me $10 with free shipping from arrow electronics.
When i connected the board to pc,it was already in the bootloader mode and i just used open companion to flash the firmware.All my model and settings were already there.i think it must be saved somewhere else on a different chip.I got expected version error as shown in the attached pic and i believe its because i updated it to latest opentx 2.2.3 and my SD card contents were from 2.2.2.I will update the SD card too.

[jhsa]

Well done

João

[bob195558]

Good job done !

Here is where/when I replaced my first (ATMEGA2561-16AU) chip:
(https://openrcforums.com/forum/viewtopi ... 120#p74105).

[MikeB]

Looks like pin 25, which is one of the gimbal analog signals.

Mike

[ninjazx11]

Thanks Mike.

[ninjazx11]

Good job done !

Here is where/when I replaced my first (ATMEGA2561-16AU) chip: (https://openrcforums.com/forum/viewtopi ... 120#p74105).

Thanks bob.

Your soldering looks good!! Did you use solder paste?

[bob195558]

Yes, I used the CHIP QUIK soldering paste very liberally
when soldering the new replacement chip to the board.
The solder just goes where it should be and was careful
not to leave to much solder on the chip's tabs.
I like the CHIP QUIK soldering paste a lot.