Smoked a VTX on a RaceQuadCopter and know nothing about the destroyed element - Page 1
Forum section: electronics / beginners

author: littleMax
author_rank: Contributor
timestamp: April 12, 2017, 08:55:59 pm
content: Hi,i'm Max and I am from germany. I just joind the forum cause i thought the EEVblog is a good place to find help with small elektronics.I build a so called RaceQuad and had done the last soldering today, the RX was the last part that was missing. But after i pluged in the battery i saw some smoke, it was the second time but the first time with the RX in place. After en examination i found the little black spot at the VTX.Now i just want to know what purpose the part has that went down the drain, and what exactly it is.You can see it on the right side of the board, right of the coil, it has 6 legs and the middle one of the top 3 got a little bit hot.Can anybody help me?

author: ovnr
author_rank: Frequent Contributor
timestamp: April 12, 2017, 09:07:09 pm
content: 80% sure it's a buck converter. If you got a few clearer images of it - including the writing on top - itmightbe possible to figure it out.You've likely wired something incorrectly, or given it a higher voltage than it is meant to run at. What model is it?

author: littleMax
author_rank: Contributor
timestamp: April 12, 2017, 09:54:43 pm
content: The VTx is an foxeer TM25 and i should handle 7-24 V, i used 4s LiPo so 14-17V.On part it says 't9G61K'

author: amyk
author_rank: Super Contributor
timestamp: April 13, 2017, 02:06:53 am
content: Quote from: littleMax on April 12, 2017, 09:54:43 pmThat would be anFR9702.

author: littleMax
author_rank: Contributor
timestamp: April 13, 2017, 05:18:21 pm
content: I checked the connections and kabels, but i cant find a real problem. The Input voltage couldnt be to high for the converter, it came directly from the 4S LiPo Battery. The damaged/overheated pin is Pin 5, Vin, it is not shorted to ground (changing Ohms from 180 to 30, maybe because of the caps).Was it maybe only bad luck? Is the convert not of good quality? Could be more damaged then only the converterIt could also be that i forget to cenect the antenna... i dont know it anymore i was to much in panic. Could this have also that result?Oh and can somebody help me to find a replacement, i looked at two local Online Shops, conrad.de and rs-online.com, also i looked at mouser.de (pretty expensive when it comes to shipping).I maybe could also use a SOT23-5 cause on the board they dont use pin 4 (EN) it is bridged to pin 5 (VIN) via a 100kOhm resistor and i read on similar datasheets that this means allways on.

author: james_s
author_rank: Super Contributor
timestamp: April 13, 2017, 06:16:18 pm
content: Did you somehow connect it backwards?You may have got lucky, but often when a buck converter fails, the full input voltage appears on the output and fries anything else in the circuit it is powering. Whether that happens or not depends on what shorts.

author: littleMax
author_rank: Contributor
timestamp: April 14, 2017, 08:43:11 am
content: It could have been possible to connect the power plug the wrong way around, but I checked the plug two times.But still for safety I did now change the wire position. Its is now red(Vcc), black(GND) and then yellow(Vsens); so reversing the plug does not put power to the ground. (picture shows old configuration.I don't see any smoked parts after the converter, so I hope it is fine :/

author: ovnr
author_rank: Frequent Contributor
timestamp: April 14, 2017, 09:25:04 am
content: It does look like there are a number of parts with the same specs and pinout:AOZ1280AP5100RT8259MP2359Theyshouldall work, but no guarantees (same Vfb, Fsw, input voltage, etc). You may be able to find them elsewhere too.Good luck.(Edit: You can find all of these on eBay, but I don't really recommend buying semiconductors there. TheMP2359is the cheapest option.)