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SX Tech chip getting hot — Parallax Forums

SX Tech chip getting hot

JonathanJonathan Posts: 1,023
edited 2005-10-11 22:52 in General Discussion
Hi All,

I just got an SX key and SX tech board. I was playing with it all day yesterday (phew, too hard for my lil brain) and got it displaying data on a serial LCD.

Today when I go to play with it, the editor can't find the SX key on com 1. I take a look, and the regulator and chip are smoking hot! I check everything, disconnect the LCD and try again.

The chip gets hot quick. The voltage is sagging on both VIN and VDD. Swap chips and the same thing happens. Without a chip in the SX tech board, the editor finds the SX key but of course comlpains about the lack of a chip, so at least I don't think the SX key is shot.

So, the bottom line is that with a chip in the SX tech but nothing else connected to it, the chip gets smoking hot real quick like. Two chips do the same. The circuit had been used for many hours the day before, no problem. No changes were made to anything. With just the SX key and no chip in the socket, no voltage sag or reg. overheating. Slide in a chip and things get hot. Any ideas on this one?

Thanks!

Jonathan

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www.madlabs.info - Home of the Hydrogen Fuel Cell Robot

Comments

  • BeanBean Posts: 8,129
    edited 2005-09-19 18:16
    Jonathan,
    Check the voltage at the SX chip. I should be 5.0Volts. If it is you must have something shorted somewhere.
    Bean.

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    ·
  • JonathanJonathan Posts: 1,023
    edited 2005-09-19 18:39
    Bean,

    There is nothing connected to short out. Looking at the board, the only thing I see that could be shorted is the filter cap.

    Thanks for the help,

    Jonathan

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-09-19 19:00
    Jonathan,

    ·· Your circuit that was running is no longer connected to the SX board?· Were both chips connected to the circuit prior to the problems?

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • JonathanJonathan Posts: 1,023
    edited 2005-09-19 19:25
    Chris,

    The circuit is no longer connected. All the "circuit" was was a serial LCD, so one wire to one SX pin, and of course VDD/VSS. Not much of a circuit, and if it was hooked up incorrectly wouldn't have worked.

    The second chip has never been used or programmed. It too gets hot when I try it now. I have not allowed it to get very hot, so it should be OK. If it is a clue, the chip gets hot right in the middle.

    Thanks,

    Jonathan

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
  • Jon WilliamsJon Williams Posts: 6,491
    edited 2005-09-19 19:46
    Are you enabling the pull-ups on unused pins?

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    Jon Williams
    Applications Engineer, Parallax
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-09-19 19:54
    Well for the second chip, the answer would be no since it has never been programmed. Good point Jon, I was thinking maybe something happened with his board, but 20 floating inputs·may consume a significant amount of current and therefore produce alot of heat.

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    ·1+1=10
  • JonathanJonathan Posts: 1,023
    edited 2005-09-20 20:03
    Jon, All,

    No, I am not enabling the pullups. I would try that, but I can't seem to program. If the SX tech board is connected to the SX key, the editor complains that it can't find the SX key. If the SX tech baord is not connected to the key, I get an error that the chip can't be found.

    Jonathan

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-09-20 20:05
    Jonathan,

    ·· Call Tech Support between 7A and 5P pacific time.· Our staff will try to determine what's going on.· Have your setup ready when you call please.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • ElectronegativityElectronegativity Posts: 311
    edited 2005-09-21 17:22
    Does the regulator get hot if you plug the board in with no chip in the socket?
    If so, then there is a short on the board.

    If not then are you sure you're not putting the chip in backwards?

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    I wonder if this wire is hot...
  • ElectronegativityElectronegativity Posts: 311
    edited 2005-10-11 15:19
    I think I figured this out.

    I had an SX20 get so hot over the weekend that it desoldered itself from my prototype board!

    I believe this occurs when the chip is clocked both internally and externally by the SX key.

    This can happen if you have a program running on an internal clock and then plug in the SX key without first turning off the power.

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    I wonder if this wire is hot...
  • Tony LeylandTony Leyland Posts: 71
    edited 2005-10-11 22:52
    Hi,

    I have had very similar problems with my SX-Tech board. I've burnt out about 4 SX-28 chips when all
    I've got connected is a resistor and an LED ! When I connect the power the green power LED on the board
    itself goes dim. Then the SX gets very hot and dies. All is well after a new SX is put in.

    I put it down to me using a very bad PSU that was transformer based and said it was 9V but sometimes
    it went to 15V. Have now started using a 9V one which is 'switched mode' and will deliver 9V constantly.

    I've had no problems since.

    Tony
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