I recently received the parts for a new build, one of which is the MAMBA F405 FC/ESC stack. I soldered up the motors then did a continuity test (or rather a resistance test because my multimeter doesn't have a continuity test), and it said there was very low resistance. I also made a smoke stopper with a 10W bulb and it lights up. I looked carefully over the whole board and I don't see any specks of solder which could be causing a short.

I tried looking online and there's not much info, but I read that sometimes there can be what looks like a short but is actually fine. I don't want to plug in a naked battery in-case there is a short and it damages something. How do I know for sure if it's normal or if it's actually dead and I have to replace it (I'm assuming Banggood's returns isn't worth the effort).

Thanks!

Hello Sambi, I would unsolder all the motors, unplug the fc and again test with the smoke stopper. It shouldn't draw many amps with nothing connected. I'm assuming you didn't connect camera and vtx.

Thanks! Yeah, I did all that but it's still the same. I took a video of it:

☹️ Don't connect directly the battery for your own safety. If you have a pc power supply you can then connect the 12v with caution. These Power supplies can prevent short circuits but be aware that the magic smoke can get out of your esc board anyway... ☹️

Looks like a short somewhere.

If your smoke stopper is truly working (not sure about what bulb that is), then there is definitely a short somewhere... ESC shouldn't draw enough current turn to turn on a bulb (as small as a 7W one) when no motors are connected.

Are you able to find out which part/chip that feels noticeably hot?

It's a 12V bulb but it's a battery with 1 dead cell so it's actually OK. I haven't tried feeling for what's hot, I'll try that.

I ended up ordering a replacement from UnmannedTech (amazingly they had the exact one i needed in stock) so will be sure to test it out before soldering anything!

Thanks for the advice.

EDIT: Ok, I just tested the new ESC (the exact same). Using my multimeter on the 'broken' ESC I get a reading of around 5.6 (ohms, I guess?). Put across the new ESC, it returns no conduction (which shows as a 1). For reference if I touch the two probes together I get 0.6.

However, the bulb still lights up if I put my smoke stopper across the nodes. I don't understand how this can be if there's no continuity between them. What's going on here?

EDIT EDIT: Nevermind, turns out I was being an idiot and getting the positive and negative the wrong way. It doesn't light up if I do it right. Still not sure why it would light up when connecting negative to positive though. Original ESC lights up positive to positive too.

(21-Feb-2019, 06:44 PM)Sambi Wrote: It's a 12V bulb but it's a battery with 1 dead cell so it's actually OK. I haven't tried feeling for what's hot, I'll try that.

I ended up ordering a replacement from UnmannedTech (amazingly they had the exact one i needed in stock) so will be sure to test it out before soldering anything!

Thanks for the advice.

EDIT: Ok, I just tested the new ESC (the exact same). Using my multimeter on the 'broken' ESC I get a reading of around 5.6 (ohms, I guess?). Put across the new ESC, it returns no conduction (which shows as a 1). For reference if I touch the two probes together I get 0.6.

However, the bulb still lights up if I put my smoke stopper across the nodes. I don't understand how this can be if there's no continuity between them. What's going on here?

EDIT EDIT: Nevermind, turns out I was being an idiot and getting the positive and negative the wrong way. It doesn't light up if I do it right. Still not sure why it would light up when connecting negative to positive though. Original ESC lights up positive to positive too.

Sometimes a reversed diode it's put on the beginning of the circuit so it shunts the power supply short circuit if you put it with reverse polarity. It's stupid but it is used widely on many equipment. It protects the equipment that you are feeding (in a bad way) but doesn't care about the supply. I don't know if that ESC board use that method but there's a chance of it 

(21-Feb-2019, 06:44 PM)Sambi Wrote: EDIT EDIT: Nevermind, turns out I was being an idiot and getting the positive and negative the wrong way. It doesn't light up if I do it right. Still not sure why it would light up when connecting negative to positive though. Original ESC lights up positive to positive too.

Wow... it's lucky that you were using the smoke stopper!!!

(21-Feb-2019, 06:44 PM)Sambi Wrote: It's a 12V bulb but it's a battery with 1 dead cell so it's actually OK. I haven't tried feeling for what's hot, I'll try that.

However, the bulb still lights up if I put my smoke stopper across the nodes. I don't understand how this can be if there's no continuity between them. What's going on here?

I know this almost a year old, but just an fyi for anyone researching info like I am.  You can safely use a 3s lipo on a 12v bulb even if all 3 cells are working, most bulbs will easily handle up to a couple volts extra for a short time, and a 3s would only put 0.7v-0.8v extra at the very most and not for long. 

I'm glad you finally figured out the cause, It actually helped me with my problem, but also, don't forget you need to factor in the watts of the bulb on your smoke stopper, not just the volts.  Don't quote me on the name, but I think it's Watts Law that states...Power (Watts) = Voltage x Current (Amps).  So a 10w bulb uses around 0.8amps or 800mah, while a 10w bulb is fine for whoops and toothpicks, some 3" builds and bigger can light the bulb just from amps pulled from a normal startup.  My rule of thumb is my builds with xt60 connectors I use smoke stopper with 25w bulb(2.1amps), and most xt30 connector builds I use a 10w bulb.