Eggfinder mini overheating?

Discussion in 'Rocketry Electronics and Software' started by JordanT, Apr 9, 2018.

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  1. Apr 9, 2018 #1

    JordanT

    JordanT

    JordanT

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    I recently built an eggfinder mini and tested it to be working quite well. I took it out of my rocket box a couple months later to show a friend and, while it wouldn't power up, it got hot. I mean too-hot-to-touch on the center pin of the GPS module and the diode at the power point. Has this happened to anyone? There doesn't appear to be any physical damage or change since it was working, and the battery connection and everything is identical. Is there a logical place to start looking, or test points I should check to see if something is straight-up fried?
     
  2. Apr 9, 2018 #2

    Keisling

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    What type of battery are you using?
     
  3. Apr 10, 2018 #3

    markkoelsch

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    Do you have a short somewhere? A soldier bridge of something like that?


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  4. Apr 10, 2018 #4

    ksaves2

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    Not good. I had a "bad"Quantum I suspect a bridge under the Wifi chip so it resides in the junk drawer. The VR chip got super hot. Kurt
     
  5. Apr 10, 2018 #5

    cerving

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    Chances are that you got a solder bridge somewhere, possibly under the RF module. That's why I put a step in the assembly instructions to put a piece of paper masking tape under the RF module and trim it to the edges. If it's a dead short between power and ground, the Mini "will" work, but it's going to suck a lot of power out of the battery, possibly overloading the regulator. Worst case, that can lead to a regulator failure, which might send the full battery voltage to your GPS and RF modules. That's a bad thing... they will fry for sure. I would recommend carefully unsoldering the RF module and looking for anything that might be causing a problem.
     
  6. Apr 16, 2018 #6

    JordanT

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    Thanks for the replies - I've been afk for a bit due to work. I've also just gotten a new multimeter (the old one died) and will be be able to check some test points. Battery is a 2s lipo, good voltage on both cells with two testers, that isn't overheating or appearing to have any other issue.

    I will double check the RF module. Edit - I subbed electrical - tape for the masking under the RF module as I was concerned about long term stability of masking tape, but that shouldn't be the problem.

    The thing that's bugging me is that it managed to checkout fine after assembly. I even set it on my deck and drove around the neighborhood to see what kind of range I could expect and how it compared to my 70cm GPS unit. I've been trying to think what could have caused a good unit to go short and all I can think is that shrink-wrapping the battery to the board might have compressed something.

    Hopefully I'll get to do a checkout this weekend and will report back if I find where it went of the rails. Thanks again!
     
    Last edited: May 6, 2018
  7. May 6, 2018 #7

    JordanT

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    The tape under the RF module looked fine (it was electrical though, not masking). I damaged most of the solder pads beyond repair during disassembly, but went ahead and tried a couple power tests. I put 7.8v on the board without the RF module and it drew 6-8mA. I put 3.3v on the RF module and it drew 250ma and the IC on the module got too hot to touch in a bit over 10 seconds. There was no visible physical damage to any of the chips. I'm at a bit of a loss for chasing down anything else, and I think I'll just order another and chalk it up to experience.
     
  8. May 8, 2018 #8

    ksaves2

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    Good idea. I have a few items in a junk cup in case I need a push button switch or LED off a dead board. You can wrack yourself trying to fix some of this stuff and it's not worth your time. Yeah, if you have a few thousands of dollars worth of SMT "diddling" equipment a piece o' cake but sometimes one just has to cut their loses.

    Geez, there's a video out there of a guy who obviously has invested a pile of money in a soldering station and microscope who put 64Gb of memory on the OOP Nexus 7 2013. I can't find the vid at the moment but a Russian guy did it too. Kurt
     
  9. May 8, 2018 #9

    cerving

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    FYI, it's not unusual for the regulator IC to get warm... it basically dissipates the power difference between the input and output power as heat. It's rated to about 1A and 16V input, although the Eggfinder circuitry itself only draws about 70 mA, so a 2S LiPo can be expected to dissipate about (7.8V - 3.3V) * .070A, or about .32W. That's not a lot, but a short will send that way up. The operational junction temperature on the regulator is rated to 125C, so it can easily be hot to the touch without being a problem.

    If the RF Module or GPS Module, or any other component on the board for that matter, is hot to the touch... well, that's a problem.
     
  10. May 11, 2018 #10

    JordanT

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    Yeah, what keeps tripping me up is that it worked 100% after I'd finished it. It was 2 months later when I got it out for a demo that it would no longer show that it was activated (no lights on the unit at all) and the extra heat, esp in the RF board IC. It's really NBD; besides, the second one is always faster to assemble. ;-)
     
  11. Feb 5, 2019 #11

    rocketgreenhouse

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    I'm in a similar boat here, RF module seems to be dead with no signs as to why. Was initially working when first assembled but died a few weeks later. Managed to save the solder pads while desoldering the RF module and the GPS module still gets a fix with the 1S led flashing. I'll probably just get a new radio module instead of a whole GPS board.
     
  12. Feb 5, 2019 #12

    BLH

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    I have had allot of luck getting GPS and Radio SMT parts removed from PCB's without wrecking the pads on the PCB or the device itself by using a feeler gauge... The kind that has a whole bunch of "blades" of different thickness ranging from 0.001 to say 0.050 inches thick. You might find a cheap one at a garage sale or something.

    Then I pick a thin one in the 0.002-0.003 range and heat one solder joint at a time and slide the blade under the joint. Just carefully keep going one solder joint at a time working the blade under the joints as you go... Only works if there are no other parts blocking the path, but does work and is cheaper than a rework station...

    Just a thought.
     
  13. Feb 5, 2019 #13

    NickG

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    This happened to me on my first Eggfinder build. Not sure what happened, but I suspect that a microscopic filing or copper strand got lodged under the RF module component or PCB.

    I put a piece of masking tape over subsequent units to protect from conductive FOD. Haven’t had a problem since.
     

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