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Thread: Issue with custom Teensy 3.2

  1. #1
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    Issue with custom Teensy 3.2

    Hi,

    I just finished putting my first custom Teensy board together tonight. I took a deep breath, plugged it in and.......nothing.

    As far as I can tell my MKL04 (from PJRC), isn't alive. It's got power, but the RESET pin is showing 0.095 volts, and it doesn't go LOW when I press my PROG button. What do I now? I'm guessing it must be something I screwed up related to using a 4 pin USB B connector instead of 5 pin, or perhaps some simplification I've made. I was hoping someone could have a peak at my schematic and see if they can spot anything.

    Regards,
    Rob
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  2. #2
    Senior Member Constantin's Avatar
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    Is there a particular reason you connected PTA6 on the MKL04 and PTA1 on the Teensy to GND? If USB-hosting is of interest, these wires should be attached to the ID pin of a 5-pin USB connector.

    However, the connector you chose has no ID pin. So PTA6/PTA1 should only be connected to each other.

    I hope you didn't burn out the MKL04 in the process of trying to flash the teensy.

    If there is a way to just connect those two pins to each other, then I'd try that first.

    Otherwise, you may have to spin a new board.

  3. #3
    Senior Member PaulStoffregen's Avatar
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    Currently that connection isn't used. Future bootloader versions may make use of it, so you should connect as documented.

  4. #4
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    Quote Originally Posted by Constantin View Post
    Is there a particular reason you connected PTA6 on the MKL04 and PTA1 on the Teensy to GND? If USB-hosting is of interest, these wires should be attached to the ID pin of a 5-pin USB connector.

    However, the connector you chose has no ID pin. So PTA6/PTA1 should only be connected to each other.

    I hope you didn't burn out the MKL04 in the process of trying to flash the teensy.

    If there is a way to just connect those two pins to each other, then I'd try that first.

    Otherwise, you may have to spin a new board.
    Well that sucks. Definitely an issue. Luckily (?) PTA6 / PTA1 were connected to the ground plane with vias, so I simply partially drilled them out and then shoved the ends of a tiny resistor lead up the vias, and soldered them in place.

    I then tested the MKL04 again, and it's the same story. I replaced the MKL04 with a shiny new old, and it now drops LOW when I hold down the PROG button, so I'm making progress.

    Unfortunately nothing else is happening. Do you think I could have fried the MPC, too?

  5. #5
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    I've replaced MK20 as well, but still no love. Testing with my multimeter, I can see that Pin 34 on the MK20 goes low when I press and hold the PROG button. After I release it, it jumps up to 3.3v briefly, and then goes back to 0.09v. So I'm pretty sure the MKL04 is doing its job, but something else is not right. Does anyone have any suggestion as to where I should be looking next?

  6. #6
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    In my schematic, I have VREF_OUT running though a resistor and then to ground. That's probably my problem. Is that going to fry the MK20? I should probably just leave pin 17 unconnected?

  7. #7
    Senior Member Constantin's Avatar
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    I went over the schematic and see no issues with the connections between the MKL04 and the MCU. I would double-check them with a DMM (as well as to GND and 3.3V). Don't use the buzzer feature, just plain old resistance.

    Wondering though why VREFOUT was tied to GND. There is no resistor. It's a short per your diagram up top. Leave VREFOUT floating or put a cap on it like Paul did. The short in your design may or may not have burned something out. Depending on how difficult it is to undo that connection, your best bet may be to lift the VREFOUT processor leg in question off the pad. If you have a new processor to plop in, it may be easiest to simply bend the affected leg up before soldering the pads.
    Last edited by Constantin; 04-17-2017 at 03:31 PM.

  8. #8
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    I replaced and amputated the MK20 and....Success! I can't thank-you enough, Constantin, for your help with this issue as well as guidance in other threads. I can now comfortably order the next revision of my board. If you're willing to have a look at my "polished" layout, let me know and I'll post it here.

  9. #9
    Senior Member Constantin's Avatar
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    I'm glad I could help, have been helped here by others far more intelligent and experienced than I so many times... which is why this community is so dear to my heart.

    If I happen to see an update, I'll be happy to review it, just keep in mind that my time here can be lumpy - intense periods followed by long absences. So if I don't see it or reply, don't think I'm ignoring it, I may have simply missed the post.

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