Repairing Taranis Plus

[andrewju]

Hi All,

A friend of mine tried to adjust the sticks on his X9D+ while the radio was switched on (this surely wasn't his best idea!)... A switch fell out of its place and touched something - presumably on the mainboard. Since then, the radio doesn't work. It doesn't power on with the switch. It doesn't react when connected via USB, and PC doesn't see it as a device either.

I'm trying to help and repair it... So far I checked the voltage regulator on the mainboard. There is 3.3v on its output, so it looks to be fine.

I'd appreciate any hints on what else to look for...

[andrewju]

Following Mike's advise from an earlier thread, I'm checking the Plus board.
BTW, the Plus and non-Plus boards have much more similarities than I thought!

Ok, the strange thing is that the junction of R57 and D2 is always low (0.0v to 0.15v), regardless of the power switch state. The 3.3v on the "other" end of R57 disappears when the power switch is OFF. It means the power doesn't reach the voltage regulator when power switch if OFF (also confirmed by the multimeter).

Also, it looks like Q2 is always closed...

[andrewju]

When connected via USB, the junction of R57 and D2 works "as expected" (0.15v when the power switch is ON, and about 3.3v when OFF). Though, there's nothing on the screen and the PC doesn't detect any new devices.

[MikeB]

When you just plug in the USB (power switch off), it seems you are getting 3.3V on the main power rail.
All that then needs to be working is the processor, the main crystal and the connections to the USB in order to get a response.
The crystal is on pins 12 and 13 and should be oscillating at 12 MHz.
If you don't get a response from the USB, then I would guess the processor has been damaged.

Mike.

[andrewju]

Thanks a lot, Mike!

Is it normal that I don't get 3.3v on the main power rail when the radio is powered from the battery and the power switch is OFF?

I have a spare processor (a bit fried - it doesn't react on USB, but works well otherwise). I will put it in tonight, for testing. My concern is that there may be some other faults in the power regulation circuit...

[MikeB]

No!
Q3 is the main (P-channel mosfet) soft power switch. R54 and R55 drive the gate, switched by Q2 and D1. When you switch the power switch on, D1 pulls R55 to ground, and then Q2 should switch on to also pull R55 to ground.

Mike.

[andrewju]

Wow, thanks a lot!!!
Looks like the power switching circuit works properly on the board I have.

It just came to my mind... it doesn't make much sense to install a half-working chip (no USB) I took earlier from a non-Plus radio. I won't be able to reflash it without USB, and the screen will probably not work as there is non-Plus firmware loaded. So I'll have to wait for a new chip. I already ordered a few spare STM32F205VET6, they should arrive early next week.
I'll post back when I get them.

[jhsa]

Good luck

João

[andrewju]

New chip in, run Zadig tool to update the driver, flash the firmware and... The radio is alive!

You guys are great!

Thanks a lot!!!

[kalle123]

Good job.

Maybe next time please post some pics.

br KH

[andrewju]

I can share some photos from the previous boards.

NOTE: The whole process greatly depends on the tools and materials you have at hand. You need to have the right tools and steady hands. Otherwise, you will likely damage your board. Do not try this yourself, unless you're certain you can do it! This is not intended to be a guide. Not yet, anyway. I'm just sharing my experience, and this is done in very high level.

I often use some low-temperature alloy (I believe it's something like a ChipQuik, but branded differently) and a very good soldering iron with temperature regulation. Soldering station would even be better.

First of all, I put some ChipQuik-alike alloy and a fair amount of flux on the chip's legs. Then warm it up with the soldering iron, so that ChipQuik will mix with the solder on the board. Unfortuantely, I don't have a photo here, but all the legs need to be covered with solder. The idea is that the solder holding the chip will melt and stay liquid for some seconds, which should be enough to lift the chip off the PCB. One needs to be careful NOT TO pull the chip if it doesn't move. There's a high risk to lift some tracks off the PCB. It takes some time to warm each side of the chip before it comes off.
On the other hand, heating the chip for too long will make the tracks go off with the chip (especially on the low-quality boards). This only comes with practice...

This is the board with the chip removed:


And this is the chip just taken off the board (this one is the Atmel from ARUni board, but physically it's the same size and number of legs as the one in Taranis):



You can see lots of ChipQuik-like solder left on the chip and on the PCB. So the PCB needs to be cleaned by removing as much of this solder as possible. Solder wick is very helpful here, with some flux of course. Ideally, the board needs to have perfectly clean pads again. The photo below is not the final result, yet:




Sometimes I also have to clean the legs of the chip just removed:



It takes a lot of time and requires full concentration in order not to break the legs.
So whenever possible, I prefer to just get a new chip and solder it onto its place.



Well, this is relatively easy. I put the new chip in and take my time to align it properly (a magnifying glass helps with this!). I usually solder just one pin and recheck chip alignment. Then I solder another pin on the opposite side of the chip and recheck the alignment again. If all is good, I go on and solder all the pins. This is done with some new solder (the real one, not ChipQuik), of course. Oh, and the flux - it should always be there. The solder won't work well without it! I usually use a flux that doesn't require washing after the soldering is done. Still, I try to wash / clean the boards whenever possible (it usually is).

So I clean everything and move on to the QA. I take a close look at the legs to check for solder bridges or bad soldering. Both are not a problem to fix, but it's better to get it done before powering the board up!

The result should be something like this (this is an AR9x with the MCU I replaced earlier):




Once again, do not try to repeat this if you're not confident in your soldering skills!

[jhsa]

Where do you get the ChipQuick alike product? Any cheaper??

Thanks

João

[andrewju]

I use Rose's metal or Wood's metal sometimes. There's a comparison table on either of the links, showing the content, melting point, etc. In my area, these are sold in a specialized shops selling electronic components and related stuff. These are much cheaper than the ChipQuik, and basically do the same thing.

I guess the ChipQuik is somewhat alike one of these, but is being advertised much wider - hence, it comes at a different price.

[kalle123]

Thank you andrewju for sharing ...

[jhsa]

Thanks for the links. ChipQuick is good, but really expensive. I gotta say though, that I haven't used half of the little packet I have here..
I used it to replace the 9x processors, and also the 9x power switches.. it's a wonderful tool.
One thing we must be careful with when using this sort of stuff, is that it sends blobs of solder everywhere quite easily. Once I had a shorted cap after I replaced a chip. The culprit was a little tiny piece of ChipQuick. Good that I have measured everything for shorts before I powered the board

João

[kalle123]

I did not know the trick with low melting solder, I have to say.
But getting Rose's metal or Wood's metal as a replacement for that ChipQuick here in Germany should be difficult.
Stupid regulations.

But I think, this should do. http://www.aliexpress.com/w/wholesale-l ... ure+solder
Will order

br KH

[bob195558]

The soldering Flux that comes with ChipQuick works better then the RadioShack rosin soldering flux.
I found using the ChipQuick flux helped a lot and I have sometimes used ChipQuick Flux when doing some very delicate soldering.

Bob B.

[jhsa]

yep, that flux is excellent..

João

[andrewju]

I guess the Aliexpress link to low-temperature solder is not what ChipQuik and other metals discussed here are. The ones on aliexpress are, most likely, the regular solder, simply "low-temperature". I don't expect these to melt at under 100°C.

[jhsa]

Yep, it was also what I thought..

João

[kalle123]

This here
http://www.aliexpress.com/item/Original ... 823eb5f52d
is Sn42Bi58

and when I see that http://www.chipquik.com/store/product_i ... _id=440001

I am missing the difference.

[jhsa]

Kalle, That is also solder paste but from chipquik..
What we are talking about is this:

https://www.youtube.com/watch?v=7kyaz4Zrd78

João

[kalle123]

João. OK. Got it. http://www.chipquik.com/datasheets/SMD1.pdf

58°C That is the difference ....
Sn42Bi58 has ~120°C

So back to low melting alloy and the question, where to get.

[kalle123]

Found a source here in Germany.

http://www.tmp-loettechnik.de/

[jhsa]

I'm afraid I can't see it in the link??

João

[kalle123]

Getting old?

[jhsa]

Definitely getting old
I was looking for ChipQuik.

João

[jhsa]

Rose's metal they sell seem to have a high melting point.
And the wood's metal they advertise seems to have no description at all.. Fishy??
Or am I getting old agasin??
João

[ReSt]

Lipowitz metal 70 degree Celsius (with Cadmium)
Wood metal 71 degree (with Cadmium)
Roses metal 95 degree (Cadmium free)

Reinhard

[kalle123]

The tip with http://www.tmp-loettechnik.de/ is from here http://www.mikrocontroller.net/articles/SMD_L%C3%B6ten

OK. It not wire and you'll need lot of flux. But price is good. Could be worth to try.

br KH