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Temp probe for troubleshooting

Discussion in 'Electronic Repair' started by Russ, Feb 27, 2005.

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  1. Russ

    Russ Guest

    I read somewhere that when a IC develops a short it will start to heat up.
    So I was thinking that maybe one of the new laser type of Temp probes might
    help in troubleshooting. Are they sensitive enough? Can they isolate a
    small 1 inch square area without picking up things close by? I talked to
    one company and they said a large 12:1 or higher ration between the distance
    and spot being measured is what to look for. Any particular model or ideas
    a long this line?

    Thanks
     
  2. This doesn't seem to be particulalry useful unless you have a reverence
    thermal map of a working unit. Some parts run hotter than others under
    normal conditions. And, what is going on in the electronics will also
    affect the heat generated.

    Any significant overheating will be obvious to a reasonably well calibrated
    finger.

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  3. mike

    mike Guest

    Might wanna be careful about sticking that well calibrated finger into
    an off-line switching power supply...or Horizontal Output Transistor.
    I'll use my IR probe, thank you.

    You might find other uses for an IR probe. I use mine to find heat
    leaks in the house, in cooking, auto repair etc. Handy little gadgets.
    mike


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  4. Russ

    Russ Guest

    Mike,

    Do you think any model will work or should I buy one of the expensive ones?
    They have them from around $40.00 and up. It would be cool when working on
    a pinball if I could point my thermal laser probe at all of the transistors
    and find the one that isn't working.

    Thanks
    Russ
     
  5. Seafarer

    Seafarer Guest

    I use the finger test and have for thirty years,if you want to be more
    precise you can buy small square temp strips that you stick on top of
    the IC.Readout is the same as a medical digi.thermometer.Got some five
    years ago as they are cheap,but never used them.Use your finger tip
    away from the hot chassis.To hot to touch,it's bad!
     
  6. sofie

    sofie Guest

    If the IC gets too hot it may be a problem or fault with the associated
    circuitry..... the IC is not the only suspect here when it gets too hot.
     
  7. mike

    mike Guest

    There are a bunch of issues.
    The spot/distance ratio is critical. At the distance of measurement,
    the spot size has to be small enough to measure just the thing you want.
    But as it gets smaller, you have trouble aiming it. Even with a laser,
    there's an offset that causes parallex error. The sense spot can't be
    in the same place as the laser spot at all distances.

    Emissivity relates to how well a particular material and surface
    treatment radiates relative to a black body. Most cheapo units are
    fixed at .95. More expensive ones have a calibration adjustment, but
    that won't help if you don't know what to set it at.
    Point it at a shiny aluminum heat sink and your reading won't be
    anywhere near accurate. It's a relative measurement for similar
    materials only.

    In most cases, you have no idea what 'normal' temperature is.
    You can't tell if the problem is the device, a loose mounting bolt,
    something else causing the overheat.

    "back in the day" story alert....

    Once tried to measure the temperature of a circuit board with an early
    IR video scanner. Result was dismal because of the widly varying
    emissivities.
    Sprayed the whole board with spray-on foot powder.
    Worked great cause it normalized emissivity.
    Problem was that I couldn't wash the stuff of when I was done.
    Ended up scrapping the board...very expensive temperature test.

    Bottom line,
    I use mine more to check the temperature of my coffee when I nuke it
    prior to pouring it into the thermos. Fun toy, but relatively little
    used in electronic diagnostics.
    mike




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  8. Russ

    Russ Guest

    Mike,

    Thanks for the feedback. Another idea of mine that doesn't seem to be
    working out. I did order the Fluke temp probe, but not the IR one. I
    almost ordered the IR one but after reading your post I am glad I didn't. I
    guess I will just use the probe for coffee and tea also.

    Thanks
    Russ
     
  9. Russ

    Russ Guest

    A few times the finger thing worked real well for me. One was a pinball
    transistor It was so hot it burned my finger. I guess I was wondering if
    something more sensitive would be helpfull.
    Thanks for input
    Russ
     
  10. Russ

    Russ Guest

    Good point. Thank you.
     
  11. RonKZ650

    RonKZ650 Guest

    If you get one, get a good one. Most IR guns with 12/1 ratio will not
    work. It depends on the focal point size. Generally 12/1 guns have a
    focal point of about 3" meaning you are measuring the average
    temperature over a 3" area, plus many the laser beam is offset somewhat
    from the actual point you are measuring. Raytek makes some nice guns.
    Two that work real nice are the ST80 with 50/1, and the ST25 Autopro. I
    use the ST80 sometimes when I suspect something heating on a board but
    can't quite pinpoint it. Works nice and easy.
     
  12. Asimov

    Asimov Guest

    "Russ" bravely wrote to "All" (22 Apr 05 06:56:36)
    --- on the heady topic of "Re: Temp probe for troubleshooting"

    Ru> From: "Russ" <>
    Ru> Xref: aeinews sci.electronics.repair:46218

    Ru> A few times the finger thing worked real well for me. One was a
    Ru> pinball transistor It was so hot it burned my finger. I guess I was
    Ru> wondering if something more sensitive would be helpfull.

    A wax crayon... Wax melts just under the boiling point of water around
    180-200'F. IIRC there are even special wax mixtures calibrated for
    specific temperatures. These are used to calibrate furnaces, ovens,
    etc.

    Many ceramic capacitors are highly sensitive to radiant heat and their
    capacitance value will drift according to temperature. When used in a
    bridge or a counter even the heat from a hand can be readily detected.

    IR diodes are also sensitive to radiant heat but have to be compared
    to a known temperature.

    A*s*i*m*o*v

    .... 'Keep the smoke inside.' -- 1st Rule of Electronics.
     
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