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"Dead PIC pin"

Discussion in 'Microcontrollers' started by jeg223, Nov 13, 2007.

  1. jeg223

    jeg223 New Member

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    One of the pins on my 18F4680 just stopped working one day. The voltage read 1.4V whether set high or low and now it just reads ground. The rest of the chip seems fine. Has anyone else had this problem before?
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    PIC's are generally very sturdy devices, if you've killed a pin you've probably done something really nasty to it!.
     
  3. jeg223

    jeg223 New Member

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    I can't think of what though. Maybe a short to ground in the output high state?
     
  4. dave

    Dave New Member

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  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Possibly?, but I would imagine it takes a LOT more than that? - certainly I've abused many PIC pins over the years, and never killed one yet.
     
  6. kchriste

    kchriste New Member Forum Supporter

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    You probably drove the pin above Vdd or below Vss and allowed excessive current to flow, damaging the pin. Instead of tossing the device, determine which state (high, low or input) the pin should be in so that the PIC draws the lowest current from Vdd. Then program the pin in that state when using the PIC in a project which doesn't require that particular IO pin.
     
    Last edited: Nov 13, 2007
  7. Sceadwian

    Sceadwian Banned

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    I've fried I/O pins on an AVR before from bad wireing and they're roughly comparable in durability to PIC pins. Inductors hooked up to I/O pins can do it as well if you're not keeping track of that kind of thing. Usually the entire I/O pin isn't gone, it can typically still read high or low values even if the output driver is toasted.
     
  8. jeg223

    jeg223 New Member

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    I'm not using inductors in this project but I'll keep that in mind. I have a rat's nest with +12 and -5 running around so I think one of those got it. I hate when ICs fail quietly like that, I wish they would just catch fire so I immediately know where the problem is.
     
  9. Stellarcore

    Stellarcore New Member

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    I fried a PIC16F688 a couple of weeks ago. I was trying to get the analog to digital converter working the way I wanted so I had a power supply hooked up directly to an input pin. This would be fine, as I had the voltage well within an acceptible range and the current was set to top out at a relatively low level on the PSU. All was well and good until my friend spontaneously grabbed the current knob on the PSU and cranked it.

    I'm not sure what happened, but from that point on I couldnt program it any more. It was stuck with the current (broken) program.

    I've also fried PICs in the past by getting them too hot while soldering/desoldering.
     
  10. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    A common practice, as an added 'read protect' feature used to be to deliberately blow either the data or clock pin, so you couldn't ever enter programming mode again.

    I can only say you must be really, really, REALLY, bad at soldering to destroy a chip in that way!.
     
  11. Stellarcore

    Stellarcore New Member

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    I'm not terrible at soldering, just still getting used to surface mount soldering. Usually it results from my attempts to remove an already soldered SMT chip. I'd rather destroy the chip than risk damaging the traces on the PCB (in most cases anyways).
     
  12. RWD7980

    RWD7980 New Member

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    THe one thing i did to kill a few pins on a PIC was a reverse polarity short w/ ark..just for a moment I have Vdd and Vcc flipped... a regulator exploded in my face and the once corrected the PIC 12F690 (I think) only had 2 outputs that worked!!
     

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