I have a mystery that needs solving. I have what looks like a transistor. It has three pins which should be emitter, base, and collector. The package is labeled A129. I have tested it with a multimeter using the diode function and there is voltage through no matter how I place the meter leads. I assume it's broken. But the mystery is that it alone makes at least a single LED blink at a constant rate.

I have it hooked up to a breadboard with DC power (was trying to use a capacitor and transistor to make a blinking LED and couldn't understand why it wouldn't work, lol..) at 3.3V. If I put it to 5V it does not blink anymore. Is it not a BJT?

Update - Photos added as requested:


unidentified component

  • 1
    \$\begingroup\$ Please add a photo of the part. In general don't assume anything about what a component is or does without having a datasheet \$\endgroup\$ Commented Oct 16, 2016 at 10:49
  • \$\begingroup\$ "A" might indicate Germanium transistor. what are you doing? trying to make an accidental blinker? or burn out parts \$\endgroup\$ Commented Oct 16, 2016 at 21:05
  • \$\begingroup\$ They're not very proud of it- no manufacturer logo \$\endgroup\$ Commented Oct 17, 2016 at 9:15

1 Answer 1


It was probably a small CMOS IC that contains an RC oscillator, a counter and a MOSFET output stage with controlled current.

There is no rule that says anything with only 3 leads has to be a simple part.

Blinking LEDs contain a similar die and have only two external leads.

Here you can find a sketchy datasheet of a similar part.

enter image description here


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