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The board I'm looking at is a modem board from a fax machine.

There are 2 identical components labeled VZ1 and VZ2 on the board, both components have F175 on the face and have 2 SMC leads.

One of them has a resistor across the back pins, and they look like they might be part of the power circuitry.

VZ1 and VZ3 visible in the top left and bottom right respectively

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    \$\begingroup\$ I was going to guess a Zener, but no strip.. so maybe a TVS (bipolar) \$\endgroup\$
    – George Herold
    Mar 1, 2016 at 18:30

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VZ is sometimes used as the designator name for zener diodes. VZ1 and VZ3 look like 2-lead packages, so that fits.

Take one off the board carefully. Put a 10 kΩ resistor in series with it, then connect that combination to a power supply, like maybe 24 V. Measure the voltage across the device, flip it around, then measure the voltage again. If it is a zener diode, then it will be 700 mV or so in one direction, and some volts in the other. That latter is the zener voltage.

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  • \$\begingroup\$ I at first thought this too, but there are others labeled DZ, that are obviously through-hole Zener diodes. I'll test it with your method later tonight. \$\endgroup\$
    – Nilloc
    Mar 1, 2016 at 20:59
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Possibly a zener diode: -

enter image description here

I believe I've seen them called VZ1, VZ2 etc..

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