I built a quadcopter a few days ago and I checked with my multimeter to see if there were any shorts before plugging in the battery. Everything checks out good so I plug in the battery and the 3 ESC tones play, then I hear a very small crackling then poof... a little bit of magic smoke... So I removed the battery quick (I didn't hear the last 2 ESC tones play) and went back to my multimeter but nothing... But then I accidentally reversed the sticks (multimeter - to quad's + / multimeter + to quad's -) and the multimeter comes alive. However, when I go + to + / - to - has no tone to indicate continuity but if I reverse it, it does. 

Does anyone have an idea of what is going on?

Continuity does not have polarity. So I don't really know what is going on with your.

Even if you check for short, you still want to use a bulb smoke stopper.

Diodes are an electronic component that only allow current to flow in one direction. Your multimeter’s continuity setting puts out a voltage with a very low current. It is DC so it is polarised, ie one probe will be positive and one probe will be negative. Given this there is most likely a part of the circuit that is conduction the current on the multimeters continuity setting when (as you state) the probes are connected to the circuit in one particular order.

Also, the big fat caps (1000uf capacitors and the like) we put on these escs will represent a short circuit when they are not charged. That’s why you get that spark sound at times when you connect the battery, for the split second the cap is not charged it is a short circuit, current goes up and you hear that spark sort of sound. Milli seconds later the cap is charged up and now represents an open circuit until something down the line needs that extra current or the battery sags on a punch out of high throttle. The caps charge is now higher voltage that the battery is delivering and “assists” the sagging battery voltage to maintain the current draw. Hence low ESR caps.

God I went off topic there, sorry I work in education and can’t help myself at times.

Does the continuity beep stay on when you connect the probes in one direction? Most likely something has fried on the esc to do with the fc part as the first three beeps are the esc initializing and the last two beeps is the fc successfully talk to the esc.

Let me find a YouTube video from me shutterbug, he’s got a great explanation and possible fix for this.

Here is the YouTube video.

I’m going to try this on some of my aio whoop boards.

(15-Aug-2020, 07:14 AM)ph2t Wrote: Diodes are an electronic component that only allow current to flow in one direction. Your multimeter’s continuity setting puts out a voltage with a very low current. It is DC so it is polarised, ie one probe will be positive and one probe will be negative. Given this there is most likely a part of the circuit that is conduction the current on the multimeters continuity setting when (as you state) the probes are connected to the circuit in one particular order.

Also, the big fat caps (1000uf capacitors and the like) we put on these escs will represent a short circuit when they are not charged. That’s why you get that spark sound at times when you connect the battery, for the split second the cap is not charged it is a short circuit, current goes up and you hear that spark sort of sound. Milli seconds later the cap is charged up and now represents an open circuit until something down the line needs that extra current or the battery sags on a punch out of high throttle. The caps charge is now higher voltage that the battery is delivering and “assists” the sagging battery voltage to maintain the current draw. Hence low ESR caps.

God I went off topic there, sorry I work in education and can’t help myself at times.

Does the continuity beep stay on when you connect the probes in one direction? Most likely something has fried on the esc to do with the fc part as the first three beeps are the esc initializing and the last two beeps is the fc successfully talk to the esc.

Let me find a YouTube video from me shutterbug, he’s got a great explanation and possible fix for this.

Yes, the beep stays on when the + (on the multimeter) is on the - of the battery connector for the quad and - to the + (multimeter/connector) so basically if I swap them, the beep is continuous.

Thank you for the video but the magic smoke sort of shook me a bit... I may just take the whole thing apart to take a better look at it.

Also, just to clarify - I posted that continuity is polarised - as opposed to what voodoo said. This is the case with some DMMs. Most continuity functions on a DMM are not polarised, but some are. My DMM is polarised. Can't have myself contradicting one of the forum's legends Soz, voodoo.

Hope you sort it out Stauros - this hobby is the best and worst!

cheers,
ph2t.

(15-Aug-2020, 07:36 AM)ph2t Wrote: Also, just to clarify - I posted that continuity is polarised - as opposed to what voodoo said. This is the case with some DMMs. Most continuity functions on a DMM are not polarised, but some are. My DMM is polarised. Can't have myself contradicting one of the forum's legends Soz, voodoo.

Hope you sort it out Stauros - this hobby is the best and worst!

cheers,
ph2t.

Yes, you are correct about the diode, polarity, and continuity. In that case it does have polarity. So I have to take back some of my words. But the OP situation doesn't make sense. If there was some kind of short between diode circuit, then +/+ and - /- should have triggered continuity. But it only trigger continuity when he goes +/- and - /+. What situation would do that? Also any short should go to ground. Unless the short is in between an input and output diode, he should have gotten a positive continuity.

Possibly, if the voltage regulator is fried it could be conducive in one direction of current versus the other? This is the only thing I can think of.

OP, I know it sounds silly but smell the fc. Lol. Get up close a smell the components. Fried silicon has a distinctive smell you can’t miss. Also look for pockets or blisters in the silicon casing of the components- this is also a sign of fried silicon.

(16-Aug-2020, 02:41 AM)ph2t Wrote: Possibly, if the voltage regulator is fried it could be conducive in one direction of current versus the other? This is the only thing I can think of.

OP, I know it sounds silly but smell the fc. Lol. Get up close a smell the components. Fried silicon has a distinctive smell you can’t miss. Also look for pockets or blisters in the silicon casing of the components- this is also a sign of fried silicon.

I guess everyone has one type of fetish? Hahah I’m just playing. I left my quad at work so most likely be checking it out tomorrow or Monday. The more I think of it, I think the 5v regulator may have went out due to the puff of smoking coming from that direction...

Thank you both for the help

*I am posting this just in case it can help someone else out in the future*

So I removed everything and worked step by step until plugging everything up. There was a little bit of bad solder on the - pad for the battery connector (the top part of the solder looked good) but it was sitting on some bad solder so I re soldered it. 

With the continuity beep when reversing the wires is due to the capacitor. (found this during my research) I had to hold it for a good 3-4 seconds before the beep went away. 

Rigged a smoke stopper really quickly and plugged in the battery to only the ESC. 3 tones, no smoke. Then I plugged up the FC (this comes with a harness), check for continuity, checks out good then plugged the battery and now got 3 tones with the 2 following so ESC and FC is good. (no smoke) 
Then plugged up everything (VTX, Cam, RX), checked for continuity, smoke stopper then added battery. No smoke and it looks good.

However, I did notice the SMA connector (for the VTX) had a breakage and maybe the smoke came from there? I replaced the wire, plugged up the antenna and getting good video. 


I am assuming there was a small piece of solder that was bridging something and it may have burned up? This is possible? This is the only thing I can think of...