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1 of 5 Minty's in our class has issues and gets VERY hot.
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Please be positive and constructive with your questions and comments.

1 of 5 Minty's in our class has issues and gets VERY hot.

by Overwatch on Wed Nov 06, 2013 4:20 pm

I purchased a few MintyBoost kits for some class mates for this semesters electronics project (to show proficiency soldering).

Last night I ran an after class session where we assembled the kits. 4 of 5 worked fine.

The first thing we did was to verify the content of the kits and everything checked out. Then we all went step by step through the instructions (fantastic by the way). Everything was great until we got to testing the 5v USB pads on our first unit. Pad 1 to pad 4 read -0.3v which is obviously bad (yes the meter was oriented correctly). I popped the batteries out and picked up the unit to triple check that we had no solder bridges or shorts and the ship was so hot it stuck to my thumb. I was not quite expecting this so the unit ended up getting flung across the lab as I recoiled, causing the unit to get pulled along with it before tearing free.

All 4 other units passed their checks and assembly was finished before we went back to the first failure. I could not find any obvious issues so we started probing some things. Now I will admit that this was my first experience trying to troubleshoot a circuit, and our professor will not be available until tomorrow to help us, so there may be some obvious things that I have missed. Here was my procedure.

  • Continuity checks on pins based on the high res pictures of an unpopulated board. Confirmed there are no shorts. I'm assuming this is only a 2 sided board.
  • Compared all resistors vs a working unit. All resistors checked out.
  • Used a bench supply to charge the capacitors and check that they held a charge. Caps worked fine.

We then fed the unit 3v DC and checked the chip with a thermal probe. We used a small heat sink on the chip just in case.

  • 1-4 seconds saw a 1-5 degree C rise.
  • at 5 seconds the chip shot up to 150C before we cut the power.

I'm out of ideas at this point. Hopefully We just did something wrong and our professor can fix it tomorrow. If not I'll get some good pictures of it and see if you guys have any more ideas.

We were not brave enough to try a known good chip in the failed board, nor were we willing to risk the suspect chip in a working board.

Ian
Overwatch
 
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Re: 1 of 5 Minty's in our class has issues and gets VERY hot

by adafruit_support_bill on Wed Nov 06, 2013 5:38 pm

Something getting hot with no load usually means a misplaced part. Is the notch in the chip aligned with the notch on the silkscreen?

Post photos of the front and back of the board and we'll check the assembly.

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Re: 1 of 5 Minty's in our class has issues and gets VERY hot

by Overwatch on Wed Nov 06, 2013 6:08 pm

I don't have the board here to take photos of right now. I will get some Thursday night. I'm pretty sure the lab has access to a digital microscope. If not I'll break out my macro lens.

Yes all the components are oriented properly. As I said. All 5 kits look exactly the same at this point. All even seem identical with my multi-meter.

Ian
Overwatch
 
Posts: 5
Joined: Wed Nov 06, 2013 3:45 pm

Re: 1 of 5 Minty's in our class has issues and gets VERY hot

by Overwatch on Sun Nov 10, 2013 12:12 am

Here is a front and back of the Mintyboost

Image
Image

I re-flowed the solder a few times to make sure there were no cold joints.
Yes I do realize that there is flux EVERYWHERE. It will get cleaned up fine after we are done.

(I posted linked thumbnails because I could not find a policy on posting BIG images. I'll change them to direct img tags if needed.)
Overwatch
 
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Re: 1 of 5 Minty's in our class has issues and gets VERY hot

by adafruit_support_bill on Sun Nov 10, 2013 8:06 am

No visible problems there. Everything is in the right place and the soldering looks good. If you contact support@adafruit.com with a link to this thread we can send you out another MintyBoost kit.

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Please be positive and constructive with your questions and comments.