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I had a component in a sizable power supply open up, but I haven't had any luck identifying it. The PCB is marked with this symbol under the component: (two terminals, one on on each side)

unknown component

I never saw this thing before it failed, but it looked exactly like a failed MOV after it failed (burnt up gray disk with leads flat on each side).

However, the component is wired in series with the AC line input, on the opposite AC line from a fuse. I've never seen any varistor used like this.

The power supply does not work with this component open, but I tried jumping across the two leads, and the power supply came right up, so it was clearly carrying current before.

So what is this?

Edit: Here is how it appears in the circuit:

schematic

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    \$\begingroup\$ It's a surge suppressor. An NTC type varistor that starts out with a high resistance and when it warms up the resistance drops. Simply look up surge suppressors online. \$\endgroup\$
    – Jack Creasey
    Commented Jan 29, 2018 at 21:17
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    \$\begingroup\$ Hotdog with mustard & a pickle? \$\endgroup\$
    – Trevor_G
    Commented Jan 29, 2018 at 21:19
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    \$\begingroup\$ @JackCreasey A surge suppressor in series with a circuit doesn't make much sense in my eyes. Except it was abused as undervoltage protection. \$\endgroup\$
    – Ariser
    Commented Jan 29, 2018 at 21:33
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    \$\begingroup\$ @Trevor_G Indeed, the resemblance is uncanny. Unfortunately, that would just create more questions. \$\endgroup\$
    – Chaos
    Commented Jan 29, 2018 at 21:35
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    \$\begingroup\$ mouser.com/ds/2/600/ametherm_MM3_%200R280-DIN-1215080.pdf ....here they call them inrush surge suppressors. \$\endgroup\$
    – Jack Creasey
    Commented Jan 29, 2018 at 21:40

2 Answers 2

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It's a thermistor. It's almost certainly of the negative temperature coefficient type and being used to limit the inrush current when the device is switched on.

There are (too) many different thermistor symbols in the wild besides the IEC one. Your symbol looks like the old Japanese Industrial Standards symbol for thermistors, except for the odd blob attached to the side.

enter image description here

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Thanks to @JackCreasey and @evildemonic, I found it is most likely an "inrush current limiter" which seems to be a type of thermistor. The symbol is for a barretter, an older device with a similar purpose.

My replacement part is therefore probably an Ametherm SL15 5R007.

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