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Feather M0 basic proto not charging
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Feather M0 basic proto not charging

by the_pimaster on Fri Jan 25, 2019 10:52 pm

Hey guy, I built a little hand held gaming device (with a sharp 168x144 display board) with the mentioned board and was having a lot of fun.
I remembered that battery life was an import metric that my friend wanted in the device so I left it running. After the 3rd day it was finally off.

I plugged it in to find the charge indicator was no longer coming on. Up to this point it charged fine.
I re-wrote some of my software to get an indication of the battery voltage level. When the battery is not plugged in, I'm reading 5.8-6 volts off of pin 9. When I plug the battery in it drops to 3-3.3 volts. I tested the board with a multimeter when the battery wasn't plugged in and was getting up around the 6 volt mark.
I was worried that I had drained the battery completely dry but it is sitting at 3.5 volts which is low, but I didn't think was catastrophic for the battery (the boards cuts out when the battery gets to 3.5 right?)

I looked around and saw a post, https://forums.adafruit.com/viewtopic.php?f=24&t=104581 that reads very similar to mine. So I looked at the board and whilst my charge controller doesn't look burnt out, it does look like it has popped.
2019-01-26 13.14.26.jpg
2019-01-26 13.14.26.jpg (301.82 KiB) Viewed 113 times

I bought this board late 2017, did some quick testing to make sure I could use it but I've only just started running it regularly. I was always plugging it in to keep the battery charged though.

Thoughts?

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Re: Feather M0 basic proto not charging

by adafruit_support_mike on Sat Jan 26, 2019 2:18 am

That does look like the LiPo charger has been damaged, and the charger's output to BAT should never be higher than 4.2V.

The 5.8V to 6V reading has to come from somewhere though. What are you using as a power source for the Feather?

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Re: Feather M0 basic proto not charging

by the_pimaster on Sun Jan 27, 2019 4:11 am

I thought this was a problem with the USB hub in my monitor and a Belkin 2.1A USB wallwart.
Double checked today, only an issue on the wallwart.

Checked the voltage readout of the wallwart, getting 4-8 volts (jumping all over the place). Tested another one to make sure I was doing the test right, constant 5.1 volts.

So I'm throwing the Belkin wallwart out. Surprised it hasn't blown my headphones or battery bank.
Sorry to be a bother.
Thanks for the support.

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Re: Feather M0 basic proto not charging

by adafruit_support_mike on Mon Jan 28, 2019 1:08 am

It's no trouble on our end.

The rest of the Feather should still be okay. IIRC, the 3.3V regulator can accept input up to about 16V. The MCP73831 LiPo charger can only handle input voltages up to 6V, but that should be the only part to have sustained damage.

You can clip it loose with a pair of flush cutters and desolder what's left of the pins one at a time. If you're comfortable working with SMT parts, replacing the MCP73831 won't be too hard. SOT-23 packages are pretty easy to work with, and the chips don't cost much:

https://www.digikey.com/product-detail/ ... e=octopart

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Re: Feather M0 basic proto not charging

by the_pimaster on Mon Jan 28, 2019 9:09 pm

Thanks for the info. I bought another board because it seemed like the simplest solution but I've also bought some charge controllers and I'll give it a go. For such a tiny cost it's worth a try.

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Re: Feather M0 basic proto not charging

by adafruit_support_mike on Tue Jan 29, 2019 1:19 am

If you're new to SMT work, it isn't too bad at the size of the part in question. It's mostly a matter of knowing a few principles and tricks.

The first principle is that, at that scale, the force of gravity is much lower than any other force acting on the component. A minor bump from the tip of a soldering iron can send SMT components flying a couple of feet.

The second principle is that the dominant force in SMT work is surface tension of the molten solder. Joints pretty much form themselves if you bring clean, molten solder close enough to start wicking across the surface of the pads or pins. Flux is a must because it keeps the surfaces clean enough for surface tension to take over. The surface tension forces are stronger than gravity though, so a joint in the solder will pull components out of position.. resistors will stand up on one end (called 'tombstoning') because the metal likes that shape better than a fillet with the part sitting flat.

The third principle is that cooled joints are far stronger than anything else in the system. You'll pull the pins off a chip before a joint even starts to budge.

That means the hardest part of the process is making the first joint and having it cool with the part aligned to the pads on the PCB. It's a three-handed operation (component, solder, and iron), so that's where the tricks come in.

Start with the component still in the tape, and melt a dot of solder onto one pad. Flux the cooled joint, get the part, place it so the pin sits on the solder. Press gently on the part while you heat the solder, and let the joint form. If you're lucky, the pins will be aligned to the pads, but about half the time there will be some kind of twist.

If you need to reliagn a part, flux the joint again and touch the edge of the pad, leaving some clearance between the tip of the iron and the pin. The solder will melt (you can often watch the solid/liquid boundary move across the surface), and when the solder between the pin and the pad liquifies, you'll be able to nudge the part with a probe. Move gently, and bring the force in at an angle to the plane of the PCB. You have to apply a combination of side force to move the part, and down force to keep the pins flat to the PCB.

Pull the iron away from the pad once the part is in the correct position, but leave the probe in place to keep the part in position as the solder cools.

Once the first joint is done, the rest is easy. It's usually a good idea to make the second joint on the opposite side of the chip for good mechanical support, but that isn's strictly necessary. The rest of the joints will form quickly, and there's a technique called 'drag soldering' where you melt a big blob of solder onto the tip of the iron and literally drag it along the pins. The joints will form as the molten metal goes past.

If you end up with a solder bridge between pins, or you think the joints are too blobby, flux the area and hold a piece of solder wick to the tips of the pads, and heat the solder wick with your iron. The wick will pull solder away from the pads, and the joints will shrink to their ideal form.

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Re: Feather M0 basic proto not charging

by the_pimaster on Tue Jan 29, 2019 7:12 am

:O

Thanks for the tips. I do hope you copied and pasted that from somewhere.

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Re: Feather M0 basic proto not charging

by adafruit_support_mike on Wed Jan 30, 2019 12:47 am

Not exactly, but I do most of my prototyping with SMT parts and think they're kind of fun. People are getting more interested in them, and I've given the same suggestions enough times that I don't have to think about the information too hard.

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Re: Feather M0 basic proto not charging

by the_pimaster on Fri Feb 15, 2019 3:31 am

Just in case someone comes across this post, I was successful in the replacement of the charger chip. I de soldered the component above it accidentally and basically melted the old chip away as I couldn't get a good grip with tweezers on it whilst heating up the leads.

It doesn't look pretty but is working.

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Re: Feather M0 basic proto not charging

by adafruit_support_mike on Sat Feb 16, 2019 12:23 am

Glad to hear you got it working. Happy hacking!

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Please be positive and constructive with your questions and comments.