pondělí 22. prosince 2014

Turnigy T9X - the rescue from battery polarity reverse

I always wondered how someone could be so careless and reverse polarity when connecting the battery connector into the radio T9X. Until I installed a programmer in my radio one night and I managed to move battery connector 1 pin on the right...

After switching to the radio crackled and smoke billowed. I immediately (within perhaps 0.5 s) again turned off the radio and began to detect damage. I found that on the motherboard there are two  smoked and cracked components. The designation was illegible.

Helped the wiki site openrcforums.com and rcmania.cz. For more information on the rcgroups.com () forum and this article: 

What to do if polarity reversal happened?
  1. Immediately turn off the radio.
  2. Disconnect the battery.
  3. Do not switch on again. If you actually reverse polarity (appeared smell a fag), it will not work and may cause further damage.
  4. Open the transmitter and view critical points.
  5. If you do not have experience with soldering on electronic equipment, seek help from someone who can. Soldering SMD components is quite difficult.
  6. Gradually replace damaged components:
  • First unsolder damaged components.
  • Then, using de-soldering braid to remove excess solder stranded. I do not recommend vacuum pump, especially piston ("syringe") - can be vacuumed with a piece of tin PCB, which could partially heat release.
  • Carefully solder the new components. Beware of polarity, especially electrolytic capacitor (which always burns, so it will definitely change) can be easily confused. Electrolyte must be oriented anode (+) to the right (toward the center of the slab) while looking at a radio antenna in a normal position forward. The anode is marked on the component printed stripe.
Soldering must be done using soldering station with adjustable heat range. Temperature control should be set at about 300 ° C or a little more to be used purely melted solder and not deadburned. If you do it with a pistol (loop, transformer) soldering iron, you can blow it all straight.

Solders as short as possible and use a suitable flux for electronics - never with plumber acids (in need such as rosin, better are the so-called Flux markers). After the wash soldering flux residues from joints rubbing alcohol or isopropyl alcohol.

It is necessary to have a suitable metal  thin-tipped tweezers and a good magnifying glass, allowing to work with miniature components. I managed to accidentally unsolder small resistor with dimensions of about 1x0, 5mm. Wwithout a magnifying glass I can not even find it. I proved stereoscopic magnifier in plastic glasses headband. Allows at least partial depth perception, which is a tiny solder SMD important.

After completion of the replacement should measure the circuits they are in the correct voltage:

What components are usually destroyed?

(List them in order of estimated probabilities are down.)
  1. Tantalum capacitor CTS 22u/16V CA45-B SMD on the main board
  2. Stabilizer 5V SMD 78L05F (SOT89) on the main board
  3. 78L05 linear voltage regulator 5V / 0,1 A, TO92, on audio converter (Beep) board  
  4. 7805 TO220 plastic casing 5V stabilizer in transmitter module
  5. 6206 SMD 3.3V stabilizer  on the main board
  6. Blown tracks on the main board (usually under a flexible adhesive pad above the display on the top side of the board)
  7. 4066 circuit on the main board. Apparently serves to guide PPM output (jack - teacher / pupil) in need transmitte can be  (allegedly according to the discussions on the internet) run with this circuit removed - then connection to a second transmitter and a simulator for PC does not work.
What to do to prevent reverse polarity?

Be careful, positive (red wire) is always on the middle pin connector to the battery. Turnigy T9X has, somewhat unhappily, stocking connector "- + -". More sensible would be to be one of the outer terminals unconnected.

Or, better, provide 3-pin battery connector from the original "cage" to AA NiMh accus. If you are using one battery, just solder the cutted off cable with connector part of the "cage". If the battery turns, it is appropriate to provide second slit end of the cable and the battery connector with a suitable non-interchangeable polarity (as I have proved red JST connectors, which are common used in the batteries of smaller capacity) and let the cable permanently attached to the transmitter.

Example of damage (burned my T9X) are on appended photos.

More details and pictures are on my specialized modeller private blog (in Czech language). 


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