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Yay, me...I just got done soldering my first surface mount IC. Because I know how volatile heat can be, and with how close the tip of my iron was to the IC (especially without a socket!), I'd like to make sure I didn't inadvertently fry the IC.

Other than testing the continuity between in/outs, what are some ways to test the other pins on a breadboard before I wire the board into my project?

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  • \$\begingroup\$ Which IC chip is it? The particular logic family could help to narrow down the types of issues to look for. Such as the differences between 74LS04 (hex inverter) and a CD4009. \$\endgroup\$
    – mctylr
    Aug 11, 2012 at 3:54

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Apply a logic level to each of the inputs, and see what the outputs give. If they're inverters the output should be 0 V when you apply 5 V (or whatever your supply voltage is) to then input. Connect the input to ground and you should get 5 V out.

It's unlikely that you fry it through the heat of soldering. ICs withstand temperatures of 300 °C on all pins simultaneously for several seconds. ESD may be another issue.

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Even though if each gate in the chip gives you the correct output for a steady-state logic input, an important property of schmitt triggers that must be tested are the thresholds of its hysteresis loop.

hysteresis loop

To accurately do that, you need an oscilloscope and a signal generator though. You need to feed it with a sine-wave signal (with peaks at logic 0 and 1 voltages) and check the resulting square-wave output. State transitions of the output should happen within the limits of acceptable threshold in the datasheet.

Without a scope and signal generator, you can still check if it is functional (no guarantee on the thresholds) by forming a relaxation oscillator. Please see this link.

schmitt trigger relaxation oscillator

A functional gate should give you a square-wave output. Choose an RC combination to give a comfortably low frequency so you can check the output without a scope: either driving an LED (blinking, less than 15Hz) or connected (decoupled by a capacitor) to a speaker (buzzing/thumping, between 60Hz to 18KHz).

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