Identify this part?

[Jonnies]

Can some identify this component (attached)?
Here's what I know:
It looks like a glass diode, except it has no polarity marking.
Its about 1/8" long.
DVM ohmmeter reads open ckt in both directions.
DVM diode test reads open ckt in both directions.

Its part of an electronic control pcb for a vacuum cleaner, and something on the pcb is preventing the motor from running. When turned on, the motor will pulse for an instant, then stop. When I probed around the board and touched the voltmeter probe to this component, the motor would briefly start again (but quickly stop in a fraction of a second). So I'm thinking the problem may involve this device.

If I remove this component, the motor will not run at all (no brief pulse-on when powered up).
If I replace it with a variety of diodes - also nothing.
If I replace it with various resistances, including 0 - also nothing.

The only way I see any sign of life, however brief, from this control board is if this component is in place (in either orientation).

So it looks like a glass diode, measure like an open, but behaves differently than either. Any ideas?

Jon.

 

[dougy83]

As it's in a AC speed controller circuit, it's quite possible it's a diac. It may have a breakdown/trigger of over 30V - so if you do want to test it, connect it in series with a 10K resistor to a power supply (adjust from low to ~40V) & measure the voltage across the device (it should rise with the PSU & then drop to a few volts after it's triggered).

Trying to replace a diac with a diode or resistor won't work if the current through it is less than the trigger current of the TRIAC it's triggering.

 

[Jonnies]

Thanks, I'll try that.
Also, in looking around this site, I found that it could be a KTY84 temperature sensor (but without the polarity marking), although I would expect it would still act like a diode. Maybe my meter isn't putting enough current through it though. Will try 'sperimenting some more.