S3 inputs on scisky isn't spinning any motors when I give it throttle

S3 on scisky board is not spinning any motors I try the throttle. I tested several working motors on it. I made sure there wasn’t any short between the solder joints. The other 3 motors work just fine. Any help would be appreciated, thank you.

Maybe one of the following reasons:

  • bad or burnt FET on that motor
  • a broken trace or a bad solder joint (maybe on the FET, socket or anything between the STM and the motor plug)
  • a non working output from the STM
  • a bad 1.25mm socket

Did it work before? Can you make some close up photos?
Replacing the FET is certainly possible with the right tools - we have a rather long thread for that already here:

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I just had a bad FET on a pretty new Scisky. Not the new style board, but one of the last of the original design. I just replaced it and its working good on the bench. Waiting on some new frames to show up and give it a real test.

At first everything was working fine. I’m thinking it was my poor soldering job and I might messed something up there when I was soldering. I tested the motor on another input and it works just fine.
Also I check if there was voltage on the S3 ports and I am getting readings as well.
Here are some pictures. Thank you for your help.

Top view

Back view

Close up view to S3: top

Close up view to S3: back

Can you get a good pic of S3’s FET? the FET is the little black surface mount thing with three connections directly towards the rear of the board from the S3 solder points. It looks like it may be damaged in “Close up view to S3: top” but since only a bit of it is in the picture it’s hard to tell.

If you want to check your soldering with your multimeter, there should be no resistance between the positive S3 terminal and the positive terminals of any other motor, and no resistance between the negative terminal and the joint on FET facing the outside of the board.

I just took another look at the board I replaced the FET on and it was the new style board, but mine was S2…


So should I replace the FET on S3 with another one?

Thank you for your help!

Hi. It’s a lot easier if you post pictures directly rather than links, you tend to get more people looking and helping.
Your soldering in the last pic makes me wary of shorts and other damage. It’s still hard to see if that fet is bad, some light downwards on it for the picture would help. Did you get a burning smell ever? It’s a distinctive smell that tends to stay about.
Replacing a fet requires good soldering skills as it’s easy to cause much more damage to the board during the process. How much tiny soldering have you done and do you have a temperature controlled soldering iron?

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I will post them on here from now on. My apologies.
That’s what I was thinking as well, that there was a short but none of the soldering is touching.
There is no burning smell when I turn it on. I have done quite of bit of soldering and desoldering to the board. I probably have damaged it in more ways haha.

No need for apology :slight_smile: just makes it easier for us to help.

If you have solder wick you could try cleaning up the motor solder points and redoing them.

@las gives good advice here and so does @Chaotix. Only thing that I can add is to use appropriate rosin core wire solder that is about .33mm diameter and also use flux on everything you solder. Flux will reduce the amount of heat required to melt the solder and also produce much cleaner results in the end. There are many options in Flux and solder so be sure the flux and solder you purchase is specifically for smd work. I use mg chemicals no clean solder flux and loctite .33mm 63/37 wire solder.


Solder wire I use something like this http://www.digikey.com/product-search/en?mpart=386844&vendor=82

Excellent links @madman1412 I’ve been meaning to ask about a good recommendation for that type of flux. I have a tin of unknown Chinese flux and, though it works I wonder just how corrosive it is. Likewise the decent leaded solder, last reel I got was from Banggood believe it or not, quality Unknown :wink:

Thanks @Chaotix. I have been working on my knowledge and skills in this for almost 2 years now and still have a lot to learn. The one thing I do know though is that crappy tools get crappy results. A radio shack iron can work but the job is much easier with the proper equipment and supplies. The no clean solder flux is important because it is non conductive. The no clean part is up to you, but I always clean after soldering because I use copious amounts of flux. The solder wire with the rosin core and the very small diameter ensure that you do not need to scorch anything in order to get the solder to flow properly. One of the first tools I bought for the bench was a SMD solder station. After using a Radio Shack fire stick trying to do some repair work on these FC and botching things up I decided that the fire stick had to go and it was a necessity to have a real iron and hot air to work on this stuff. I have not regretted that one bit and that solder station is my most valuable tool on the bench. I am a carpenter by trade so to compare I will not buy a Ryobi tool because I know the money that I save over getting the cheap crap will not be worth the crappy results they yield. I look to Jet, Milwaukee, Bosch, Dewalt and other brands that have proven quality and precision results. I am not against being frugal with how I spend my money and if I am not going to use a tool very often I would weigh the benefit of using a cheap tool to do a one time job if it can do the work and get decent results. But if I need to use the tool often and need precision results, I always look to spend a little more and get the tool that has a proven track record and ensures quality results. The flux and the solder are part of the equation here and are tools to getting good clean work. I jumped right into the deep end when I started into this and wanted to know how to fix these FC. I have mainly concentrated on AlienWii since they went extinct feeling like someone needed to fix these because I knew that there would be plenty of people that did as I and tried but failed the first time. After I messed up 1 FC I decided I needed better tools and skills to do this. Now I have made and repaired many Alien FC doing replacements of various components. Gyro, Atmega, Buck Boost Chips and FETs are some of the most common. Then trace and socket/wire repairs. There usually are specific things that repeatedly happen. Reverse polarity is one of the most common as well as the FET. With the Scisky I have been able to bring a few back to life but they are easily had for 30$ and the quality is hit and miss. If one can be repaired without too much trouble I say it is worth it but I do not go out of my way to fix one. For practice and training, I say it is always worth it. I have a limited knowledge of how all the circuitry works and for the Scisky they do not really hand out the schematic or board files so you can figure out exactly what is what. If one wants to know bad enough though you can examine the board and identify all the components and visually see the traces that run under the masking and the vias etc. @las and quite a few other users here have a much better understanding of the circuitry of these cards and I think @las is the MMC authority on the Scisky with what I have seen him do with them.


@madman1412: Thank you. I still don’t like that FC - for reasons. :wink: