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Thread: Teensy 4.0 shorted permanently with GND

  1. #1
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    Teensy 4.0 shorted permanently with GND

    Pin no 21 on my Teensy 4.0 automatically got internally shorted with ground. So now irrespective of anything I program, the pin no 21 remains shorted internally. I have inspected the board and there is no external short for sure. There was an instance where I declared that pin as an output pin and gave it a 3.3v input this was via a resistor so there is no case of short circuit. What might have caused it to get shorted permanently with ground internally..? Other pins are working perfectly fine.

  2. #2
    Senior Member+ defragster's Avatar
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    That sounds odd, expect the same has been done here and other for sure in the past year since T_4 was in Beta with no ill effects. But nothing over 3.3V.

    Has a sketch compiled OverClocked been used at higher speeds than the default 600 MHz?

    Perhaps try the 15 second Button press to Restore the state of the T_4 and have the factory Blink reloaded. Then write a sketch to check the function of Pin #21 with Analog Read and write as well as Digital In and out?

  3. #3
    Senior Member PaulStoffregen's Avatar
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    Does pin 17 still work? Those 2 are routed close to each other and GND (17 is closer) on the PCB.

  4. #4
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    No I have never overclocked while uploading the sketch. I also tried pressing the button for 15 seconds the board got reset and the LED started blinking, but still my DMM showed that there was continuity between pin 21 and ground. I tired doing Digital In but that continuously shows me a '0'. I did not try Digital Out since that may short the ground and Vcc via pin 21 and burn the whole board. I also tried Analog Read it also shows me a constant 0 with some occasional 1's in between.

  5. #5
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    Yes the pin 17 still works fine and shows no continuity between pin 21 or GND. I tried Digital Out/In Analog Read everything works just perfectly fine.

  6. #6
    Senior Member PaulStoffregen's Avatar
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    DMM continuously sends a test current through whatever you're measuring, and then looks for the voltage to be below some threshold. Exactly what current and voltage vary quite a lot depending on the DMM. But the point is to understand this is an active test that transmits a current through your Teensy. It's not a passive test like measuring voltage.

    A good way to test the pin is with pinMode INPUT_PULLUP, and then measure the voltage. If the pin really is shorted to GND, using INPUT_PULLUP will cause only a very low and safe current flow inside the chip.

  7. #7
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    Yes I've tried that but pin 21 w.r.t. GND shows 0.01V and with w.r.t. Vcc is shows somewhat 3.20-3.26V. I also tried Digital Reading the pin after Input_PULLUP but it still shows 0.

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